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-rw-r--r--html/edit/001-editor.mu.html754
-rw-r--r--html/edit/002-typing.mu.html108
-rw-r--r--html/edit/003-shortcuts.mu.html3291
-rw-r--r--html/edit/004-programming-environment.mu.html52
-rw-r--r--html/edit/005-sandbox.mu.html102
-rw-r--r--html/edit/006-sandbox-copy.mu.html44
-rw-r--r--html/edit/007-sandbox-delete.mu.html36
-rw-r--r--html/edit/008-sandbox-edit.mu.html38
-rw-r--r--html/edit/009-sandbox-test.mu.html14
-rw-r--r--html/edit/010-sandbox-trace.mu.html16
-rw-r--r--html/edit/011-errors.mu.html64
-rw-r--r--html/edit/012-editor-undo.mu.html54
12 files changed, 2294 insertions, 2279 deletions
diff --git a/html/edit/001-editor.mu.html b/html/edit/001-editor.mu.html
index b9ff83f1..c5bc16a5 100644
--- a/html/edit/001-editor.mu.html
+++ b/html/edit/001-editor.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -68,10 +68,10 @@ if ('onhashchange' in window) {
 <span id="L6" class="LineNr">  6 </span>  <span class="Constant">local-scope</span>
 <span id="L7" class="LineNr">  7 </span>  <span class="Constant">load-inputs</span>
 <span id="L8" class="LineNr">  8 </span>  open-console
-<span id="L9" class="LineNr">  9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a> <span class="Constant">0/screen</span>  <span class="Comment"># non-scrolling app</span>
+<span id="L9" class="LineNr">  9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a><span class="Constant"> null/screen</span>  <span class="Comment"># non-scrolling app</span>
 <span id="L10" class="LineNr"> 10 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> text, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L11" class="LineNr"> 11 </span>  <a href='001-editor.mu.html#L107'>render</a> <span class="Constant">0/screen</span>, e
-<span id="L12" class="LineNr"> 12 </span>  <a href='../084console.mu.html#L88'>wait-for-event</a> <span class="Constant">0/console</span>
+<span id="L11" class="LineNr"> 11 </span>  <a href='001-editor.mu.html#L109'>render</a><span class="Constant"> null/screen,</span> e
+<span id="L12" class="LineNr"> 12 </span>  <a href='../084console.mu.html#L88'>wait-for-event</a><span class="Constant"> null/console</span>
 <span id="L13" class="LineNr"> 13 </span>  close-console
 <span id="L14" class="LineNr"> 14 </span>]
 <span id="L15" class="LineNr"> 15 </span>
@@ -80,7 +80,7 @@ if ('onhashchange' in window) {
 <span id="L18" class="LineNr"> 18 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
 <span id="L19" class="LineNr"> 19 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abc]</span>, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
 <span id="L20" class="LineNr"> 20 </span>  run [
-<span id="L21" class="LineNr"> 21 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L21" class="LineNr"> 21 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L22" class="LineNr"> 22 </span>  ]
 <span id="L23" class="LineNr"> 23 </span>  screen-should-contain [
 <span id="L24" class="LineNr"> 24 </span>    <span class="Comment"># top line of screen reserved for menu</span>
@@ -123,7 +123,7 @@ if ('onhashchange' in window) {
 <span id="L61" class="LineNr"> 61 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">cursor-row:offset</span>, <span class="Constant">1/top</span>
 <span id="L62" class="LineNr"> 62 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">cursor-column:offset</span>, left
 <span id="L63" class="LineNr"> 63 </span>  <span class="Comment"># initialize empty contents</span>
-<span id="L64" class="LineNr"> 64 </span>  init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> push <span class="Constant">167/§</span>, <span class="Constant">0/tail</span>
+<span id="L64" class="LineNr"> 64 </span>  init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> push <span class="Constant">167/§</span>,<span class="Constant"> null</span>
 <span id="L65" class="LineNr"> 65 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">data:offset</span>, init
 <span id="L66" class="LineNr"> 66 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">top-of-screen:offset</span>, init
 <span id="L67" class="LineNr"> 67 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">before-cursor:offset</span>, init
@@ -142,386 +142,388 @@ if ('onhashchange' in window) {
 <span id="L80" class="LineNr"> 80 </span>  <span class="Constant">local-scope</span>
 <span id="L81" class="LineNr"> 81 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">3/height</span>
 <span id="L82" class="LineNr"> 82 </span>  run [
-<span id="L83" class="LineNr"> 83 </span>    e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">0/data</span>, <span class="Constant">2/left</span>, <span class="Constant">5/right</span>
-<span id="L84" class="LineNr"> 84 </span>    2:editor/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy *e
+<span id="L83" class="LineNr"> 83 </span>    e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a><span class="Constant"> null/data,</span> <span class="Constant">2/left</span>, <span class="Constant">5/right</span>
+<span id="L84" class="LineNr"> 84 </span>    1:editor/<span class="Special">raw</span> <span class="Special">&lt;-</span> copy *e
 <span id="L85" class="LineNr"> 85 </span>  ]
 <span id="L86" class="LineNr"> 86 </span>  memory-should-contain [
-<span id="L87" class="LineNr"> 87 </span>    <span class="Comment"># 2 (data) &lt;- just the § sentinel</span>
-<span id="L88" class="LineNr"> 88 </span>    <span class="Comment"># 3 (top of screen) &lt;- the § sentinel</span>
-<span id="L89" class="LineNr"> 89 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># bottom-of-screen; null since text fits on screen</span>
-<span id="L90" class="LineNr"> 90 </span>    <span class="Comment"># 5 (before cursor) &lt;- the § sentinel</span>
-<span id="L91" class="LineNr"> 91 </span>   <span class="Constant"> 6</span> <span class="Special">&lt;-</span><span class="Constant"> 2</span>  <span class="Comment"># left</span>
-<span id="L92" class="LineNr"> 92 </span>   <span class="Constant"> 7</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># right  (inclusive)</span>
-<span id="L93" class="LineNr"> 93 </span>   <span class="Constant"> 8</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># bottom (not set until render)</span>
-<span id="L94" class="LineNr"> 94 </span>   <span class="Constant"> 9</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># cursor row</span>
-<span id="L95" class="LineNr"> 95 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 2</span>  <span class="Comment"># cursor column</span>
-<span id="L96" class="LineNr"> 96 </span>  ]
-<span id="L97" class="LineNr"> 97 </span>  screen-should-contain [
-<span id="L98" class="LineNr"> 98 </span>   <span class="Constant"> .     .</span>
-<span id="L99" class="LineNr"> 99 </span>   <span class="Constant"> .     .</span>
+<span id="L87" class="LineNr"> 87 </span>    <span class="Comment"># 1,2 (data) &lt;- just the § sentinel</span>
+<span id="L88" class="LineNr"> 88 </span>    <span class="Comment"># 3,4 (top of screen) &lt;- the § sentinel</span>
+<span id="L89" class="LineNr"> 89 </span>    <span class="Comment"># 5 (bottom of screen) &lt;- null since text fits on screen</span>
+<span id="L90" class="LineNr"> 90 </span>   <span class="Constant"> 5</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L91" class="LineNr"> 91 </span>   <span class="Constant"> 6</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L92" class="LineNr"> 92 </span>    <span class="Comment"># 7,8 (before cursor) &lt;- the § sentinel</span>
+<span id="L93" class="LineNr"> 93 </span>   <span class="Constant"> 9</span> <span class="Special">&lt;-</span><span class="Constant"> 2</span>  <span class="Comment"># left</span>
+<span id="L94" class="LineNr"> 94 </span>   <span class="Constant"> 10</span> <span class="Special">&lt;-</span><span class="Constant"> 4</span>  <span class="Comment"># right  (inclusive)</span>
+<span id="L95" class="LineNr"> 95 </span>   <span class="Constant"> 11</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>  <span class="Comment"># bottom (not set until render)</span>
+<span id="L96" class="LineNr"> 96 </span>   <span class="Constant"> 12</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>  <span class="Comment"># cursor row</span>
+<span id="L97" class="LineNr"> 97 </span>   <span class="Constant"> 13</span> <span class="Special">&lt;-</span><span class="Constant"> 2</span>  <span class="Comment"># cursor column</span>
+<span id="L98" class="LineNr"> 98 </span>  ]
+<span id="L99" class="LineNr"> 99 </span>  screen-should-contain [
 <span id="L100" class="LineNr">100 </span>   <span class="Constant"> .     .</span>
-<span id="L101" class="LineNr">101 </span>  ]
-<span id="L102" class="LineNr">102 </span>]
-<span id="L103" class="LineNr">103 </span>
-<span id="L104" class="LineNr">104 </span><span class="Comment"># Assumes cursor should be at coordinates (cursor-row, cursor-column) and</span>
-<span id="L105" class="LineNr">105 </span><span class="Comment"># updates before-cursor to match. Might also move coordinates if they're</span>
-<span id="L106" class="LineNr">106 </span><span class="Comment"># outside text.</span>
-<span id="L107" class="LineNr">107 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor<span class="muRecipe"> -&gt; </span>last-row:num, last-column:num, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor [
-<span id="L108" class="LineNr">108 </span>  <span class="Constant">local-scope</span>
-<span id="L109" class="LineNr">109 </span>  <span class="Constant">load-inputs</span>
-<span id="L110" class="LineNr">110 </span>  <span class="muControl">return-unless</span> editor, <span class="Constant">1/top</span>, <span class="Constant">0/left</span>
-<span id="L111" class="LineNr">111 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
-<span id="L112" class="LineNr">112 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
-<span id="L113" class="LineNr">113 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
-<span id="L114" class="LineNr">114 </span>  <span class="Comment"># traversing editor</span>
-<span id="L115" class="LineNr">115 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L116" class="LineNr">116 </span>  <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
-<span id="L117" class="LineNr">117 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L118" class="LineNr">118 </span>  <span class="Comment"># traversing screen</span>
-<span id="L119" class="LineNr">119 </span>  color:num <span class="Special">&lt;-</span> copy <span class="Constant">7/white</span>
-<span id="L120" class="LineNr">120 </span>  row:num <span class="Special">&lt;-</span> copy <span class="Constant">1/top</span>
-<span id="L121" class="LineNr">121 </span>  column:num <span class="Special">&lt;-</span> copy left
-<span id="L122" class="LineNr">122 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
-<span id="L123" class="LineNr">123 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
-<span id="L124" class="LineNr">124 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L125" class="LineNr">125 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
-<span id="L126" class="LineNr">126 </span>  <span class="Delimiter">{</span>
-<span id="L127" class="LineNr">127 </span><span class="Constant">    +next-character</span>
-<span id="L128" class="LineNr">128 </span>    <span class="muControl">break-unless</span> curr
-<span id="L129" class="LineNr">129 </span>    off-screen?:bool <span class="Special">&lt;-</span> greater-or-equal row, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L130" class="LineNr">130 </span>    <span class="muControl">break-if</span> off-screen?
-<span id="L131" class="LineNr">131 </span>    <span class="Comment"># update editor.before-cursor</span>
-<span id="L132" class="LineNr">132 </span>    <span class="Comment"># Doing so at the start of each iteration ensures it stays one step behind</span>
-<span id="L133" class="LineNr">133 </span>    <span class="Comment"># the current character.</span>
-<span id="L134" class="LineNr">134 </span>    <span class="Delimiter">{</span>
-<span id="L135" class="LineNr">135 </span>      at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
-<span id="L136" class="LineNr">136 </span>      <span class="muControl">break-unless</span> at-cursor-row?
-<span id="L137" class="LineNr">137 </span>      at-cursor?:bool <span class="Special">&lt;-</span> equal column, cursor-column
-<span id="L138" class="LineNr">138 </span>      <span class="muControl">break-unless</span> at-cursor?
-<span id="L139" class="LineNr">139 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L140" class="LineNr">140 </span>    <span class="Delimiter">}</span>
-<span id="L141" class="LineNr">141 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
-<span id="L142" class="LineNr">142 </span><span class="Constant">    &lt;character-c-received&gt;</span>
-<span id="L143" class="LineNr">143 </span>    <span class="Delimiter">{</span>
-<span id="L144" class="LineNr">144 </span>      <span class="Comment"># newline? move to left rather than 0</span>
-<span id="L145" class="LineNr">145 </span>      newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
-<span id="L146" class="LineNr">146 </span>      <span class="muControl">break-unless</span> newline?
-<span id="L147" class="LineNr">147 </span>      <span class="Comment"># adjust cursor if necessary</span>
-<span id="L148" class="LineNr">148 </span>      <span class="Delimiter">{</span>
-<span id="L149" class="LineNr">149 </span>        at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
-<span id="L150" class="LineNr">150 </span>        <span class="muControl">break-unless</span> at-cursor-row?
-<span id="L151" class="LineNr">151 </span>        left-of-cursor?:bool <span class="Special">&lt;-</span> lesser-than column, cursor-column
-<span id="L152" class="LineNr">152 </span>        <span class="muControl">break-unless</span> left-of-cursor?
-<span id="L153" class="LineNr">153 </span>        cursor-column <span class="Special">&lt;-</span> copy column
-<span id="L154" class="LineNr">154 </span>        before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
-<span id="L155" class="LineNr">155 </span>      <span class="Delimiter">}</span>
-<span id="L156" class="LineNr">156 </span>      <span class="Comment"># clear rest of line in this window</span>
-<span id="L157" class="LineNr">157 </span>      <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L158" class="LineNr">158 </span>      <span class="Comment"># skip to next line</span>
-<span id="L159" class="LineNr">159 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L160" class="LineNr">160 </span>      column <span class="Special">&lt;-</span> copy left
-<span id="L161" class="LineNr">161 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
-<span id="L162" class="LineNr">162 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L163" class="LineNr">163 </span>      <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L164" class="LineNr">164 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
-<span id="L165" class="LineNr">165 </span>    <span class="Delimiter">}</span>
-<span id="L166" class="LineNr">166 </span>    <span class="Delimiter">{</span>
-<span id="L167" class="LineNr">167 </span>      <span class="Comment"># at right? wrap. even if there's only one more letter left; we need</span>
-<span id="L168" class="LineNr">168 </span>      <span class="Comment"># room for clicking on the cursor after it.</span>
-<span id="L169" class="LineNr">169 </span>      at-right?:bool <span class="Special">&lt;-</span> equal column, right
-<span id="L170" class="LineNr">170 </span>      <span class="muControl">break-unless</span> at-right?
-<span id="L171" class="LineNr">171 </span>      <span class="Comment"># print wrap icon</span>
-<span id="L172" class="LineNr">172 </span>      wrap-icon:char <span class="Special">&lt;-</span> copy <span class="Constant">8617/loop-back-to-left</span>
-<span id="L173" class="LineNr">173 </span>      print <a href='../081print.mu.html#L16'>screen</a>, wrap-icon, <span class="Constant">245/grey</span>
-<span id="L174" class="LineNr">174 </span>      column <span class="Special">&lt;-</span> copy left
-<span id="L175" class="LineNr">175 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L176" class="LineNr">176 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
-<span id="L177" class="LineNr">177 </span>      <span class="Comment"># don't increment curr</span>
-<span id="L178" class="LineNr">178 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
-<span id="L179" class="LineNr">179 </span>    <span class="Delimiter">}</span>
-<span id="L180" class="LineNr">180 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c, color
-<span id="L181" class="LineNr">181 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L182" class="LineNr">182 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L183" class="LineNr">183 </span>    column <span class="Special">&lt;-</span> add column,<span class="Constant"> 1</span>
-<span id="L184" class="LineNr">184 </span>   <span class="muControl"> loop</span>
-<span id="L185" class="LineNr">185 </span>  <span class="Delimiter">}</span>
-<span id="L186" class="LineNr">186 </span>  <span class="Comment"># save first character off-screen</span>
-<span id="L187" class="LineNr">187 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">bottom-of-screen:offset</span>, curr
-<span id="L188" class="LineNr">188 </span>  <span class="Comment"># is cursor to the right of the last line? move to end</span>
-<span id="L189" class="LineNr">189 </span>  <span class="Delimiter">{</span>
-<span id="L190" class="LineNr">190 </span>    at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
-<span id="L191" class="LineNr">191 </span>    cursor-outside-line?:bool <span class="Special">&lt;-</span> lesser-or-equal column, cursor-column
-<span id="L192" class="LineNr">192 </span>    before-cursor-on-same-line?:bool <span class="Special">&lt;-</span> and at-cursor-row?, cursor-outside-line?
-<span id="L193" class="LineNr">193 </span>    above-cursor-row?:bool <span class="Special">&lt;-</span> lesser-than row, cursor-row
-<span id="L194" class="LineNr">194 </span>    before-cursor?:bool <span class="Special">&lt;-</span> or before-cursor-on-same-line?, above-cursor-row?
-<span id="L195" class="LineNr">195 </span>    <span class="muControl">break-unless</span> before-cursor?
-<span id="L196" class="LineNr">196 </span>    cursor-row <span class="Special">&lt;-</span> copy row
-<span id="L197" class="LineNr">197 </span>    cursor-column <span class="Special">&lt;-</span> copy column
-<span id="L198" class="LineNr">198 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L199" class="LineNr">199 </span>  <span class="Delimiter">}</span>
-<span id="L200" class="LineNr">200 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">bottom:offset</span>, row
-<span id="L201" class="LineNr">201 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
-<span id="L202" class="LineNr">202 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L203" class="LineNr">203 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L204" class="LineNr">204 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L205" class="LineNr">205 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L206" class="LineNr">206 </span> <span class="muControl"> return</span> row, left/column
-<span id="L207" class="LineNr">207 </span>]
-<span id="L208" class="LineNr">208 </span>
-<span id="L209" class="LineNr">209 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L209'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, row:num, column:num, left:num, right:num<span class="muRecipe"> -&gt; </span><a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
-<span id="L210" class="LineNr">210 </span>  <span class="Constant">local-scope</span>
-<span id="L211" class="LineNr">211 </span>  <span class="Constant">load-inputs</span>
-<span id="L212" class="LineNr">212 </span>  <span class="Comment"># if it's the real screen, use the optimized primitive</span>
-<span id="L213" class="LineNr">213 </span>  <span class="Delimiter">{</span>
-<span id="L214" class="LineNr">214 </span>    <span class="muControl">break-if</span> <a href='../081print.mu.html#L16'>screen</a>
-<span id="L215" class="LineNr">215 </span>    clear-display-from row, column, left, right
-<span id="L216" class="LineNr">216 </span>   <span class="muControl"> return</span>
-<span id="L217" class="LineNr">217 </span>  <span class="Delimiter">}</span>
-<span id="L218" class="LineNr">218 </span>  <span class="Comment"># if not, go the slower route</span>
-<span id="L219" class="LineNr">219 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
-<span id="L220" class="LineNr">220 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L221" class="LineNr">221 </span>  <a href='001-editor.mu.html#L224'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
-<span id="L222" class="LineNr">222 </span>]
-<span id="L223" class="LineNr">223 </span>
-<span id="L224" class="LineNr">224 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L224'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, row:num, left:num, right:num<span class="muRecipe"> -&gt; </span><a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
-<span id="L225" class="LineNr">225 </span>  <span class="Constant">local-scope</span>
-<span id="L226" class="LineNr">226 </span>  <span class="Constant">load-inputs</span>
-<span id="L227" class="LineNr">227 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L228" class="LineNr">228 </span>  <span class="Comment"># if it's the real screen, use the optimized primitive</span>
-<span id="L229" class="LineNr">229 </span>  <span class="Delimiter">{</span>
-<span id="L230" class="LineNr">230 </span>    <span class="muControl">break-if</span> <a href='../081print.mu.html#L16'>screen</a>
-<span id="L231" class="LineNr">231 </span>    clear-display-from row, left, left, right
-<span id="L232" class="LineNr">232 </span>   <span class="muControl"> return</span>
-<span id="L233" class="LineNr">233 </span>  <span class="Delimiter">}</span>
-<span id="L234" class="LineNr">234 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, left
-<span id="L235" class="LineNr">235 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
-<span id="L236" class="LineNr">236 </span>  <span class="Delimiter">{</span>
-<span id="L237" class="LineNr">237 </span>    at-bottom-of-screen?:bool <span class="Special">&lt;-</span> greater-or-equal row, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L238" class="LineNr">238 </span>    <span class="muControl">break-if</span> at-bottom-of-screen?
-<span id="L239" class="LineNr">239 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, left
-<span id="L240" class="LineNr">240 </span>    <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L241" class="LineNr">241 </span>    row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L242" class="LineNr">242 </span>   <span class="muControl"> loop</span>
-<span id="L243" class="LineNr">243 </span>  <span class="Delimiter">}</span>
-<span id="L244" class="LineNr">244 </span>]
-<span id="L245" class="LineNr">245 </span>
-<span id="L246" class="LineNr">246 </span><span class="muScenario">scenario</span> editor-prints-multiple-lines [
-<span id="L247" class="LineNr">247 </span>  <span class="Constant">local-scope</span>
-<span id="L248" class="LineNr">248 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
-<span id="L249" class="LineNr">249 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
-<span id="L250" class="LineNr">250 </span><span class="Constant">def]</span>
-<span id="L251" class="LineNr">251 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L252" class="LineNr">252 </span>  run [
-<span id="L253" class="LineNr">253 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L254" class="LineNr">254 </span>  ]
-<span id="L255" class="LineNr">255 </span>  screen-should-contain [
-<span id="L256" class="LineNr">256 </span>   <span class="Constant"> .     .</span>
-<span id="L257" class="LineNr">257 </span>   <span class="Constant"> .abc  .</span>
-<span id="L258" class="LineNr">258 </span>   <span class="Constant"> .def  .</span>
-<span id="L259" class="LineNr">259 </span>   <span class="Constant"> .     .</span>
-<span id="L260" class="LineNr">260 </span>  ]
-<span id="L261" class="LineNr">261 </span>]
-<span id="L262" class="LineNr">262 </span>
-<span id="L263" class="LineNr">263 </span><span class="muScenario">scenario</span> editor-handles-offsets [
-<span id="L264" class="LineNr">264 </span>  <span class="Constant">local-scope</span>
-<span id="L265" class="LineNr">265 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
-<span id="L266" class="LineNr">266 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abc]</span>, <span class="Constant">1/left</span>, <span class="Constant">5/right</span>
-<span id="L267" class="LineNr">267 </span>  run [
-<span id="L268" class="LineNr">268 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L269" class="LineNr">269 </span>  ]
-<span id="L270" class="LineNr">270 </span>  screen-should-contain [
-<span id="L271" class="LineNr">271 </span>   <span class="Constant"> .     .</span>
-<span id="L272" class="LineNr">272 </span>   <span class="Constant"> . abc .</span>
+<span id="L101" class="LineNr">101 </span>   <span class="Constant"> .     .</span>
+<span id="L102" class="LineNr">102 </span>   <span class="Constant"> .     .</span>
+<span id="L103" class="LineNr">103 </span>  ]
+<span id="L104" class="LineNr">104 </span>]
+<span id="L105" class="LineNr">105 </span>
+<span id="L106" class="LineNr">106 </span><span class="Comment"># Assumes cursor should be at coordinates (cursor-row, cursor-column) and</span>
+<span id="L107" class="LineNr">107 </span><span class="Comment"># updates before-cursor to match. Might also move coordinates if they're</span>
+<span id="L108" class="LineNr">108 </span><span class="Comment"># outside text.</span>
+<span id="L109" class="LineNr">109 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor<span class="muRecipe"> -&gt; </span>last-row:num, last-column:num, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor [
+<span id="L110" class="LineNr">110 </span>  <span class="Constant">local-scope</span>
+<span id="L111" class="LineNr">111 </span>  <span class="Constant">load-inputs</span>
+<span id="L112" class="LineNr">112 </span>  <span class="muControl">return-unless</span> editor, <span class="Constant">1/top</span>, <span class="Constant">0/left</span>
+<span id="L113" class="LineNr">113 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
+<span id="L114" class="LineNr">114 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
+<span id="L115" class="LineNr">115 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
+<span id="L116" class="LineNr">116 </span>  <span class="Comment"># traversing editor</span>
+<span id="L117" class="LineNr">117 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L118" class="LineNr">118 </span>  <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
+<span id="L119" class="LineNr">119 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L120" class="LineNr">120 </span>  <span class="Comment"># traversing screen</span>
+<span id="L121" class="LineNr">121 </span>  color:num <span class="Special">&lt;-</span> copy <span class="Constant">7/white</span>
+<span id="L122" class="LineNr">122 </span>  row:num <span class="Special">&lt;-</span> copy <span class="Constant">1/top</span>
+<span id="L123" class="LineNr">123 </span>  column:num <span class="Special">&lt;-</span> copy left
+<span id="L124" class="LineNr">124 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
+<span id="L125" class="LineNr">125 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
+<span id="L126" class="LineNr">126 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
+<span id="L127" class="LineNr">127 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
+<span id="L128" class="LineNr">128 </span>  <span class="Delimiter">{</span>
+<span id="L129" class="LineNr">129 </span><span class="Constant">    +next-character</span>
+<span id="L130" class="LineNr">130 </span>    <span class="muControl">break-unless</span> curr
+<span id="L131" class="LineNr">131 </span>    off-screen?:bool <span class="Special">&lt;-</span> greater-or-equal row, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L132" class="LineNr">132 </span>    <span class="muControl">break-if</span> off-screen?
+<span id="L133" class="LineNr">133 </span>    <span class="Comment"># update editor.before-cursor</span>
+<span id="L134" class="LineNr">134 </span>    <span class="Comment"># Doing so at the start of each iteration ensures it stays one step behind</span>
+<span id="L135" class="LineNr">135 </span>    <span class="Comment"># the current character.</span>
+<span id="L136" class="LineNr">136 </span>    <span class="Delimiter">{</span>
+<span id="L137" class="LineNr">137 </span>      at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
+<span id="L138" class="LineNr">138 </span>      <span class="muControl">break-unless</span> at-cursor-row?
+<span id="L139" class="LineNr">139 </span>      at-cursor?:bool <span class="Special">&lt;-</span> equal column, cursor-column
+<span id="L140" class="LineNr">140 </span>      <span class="muControl">break-unless</span> at-cursor?
+<span id="L141" class="LineNr">141 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L142" class="LineNr">142 </span>    <span class="Delimiter">}</span>
+<span id="L143" class="LineNr">143 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
+<span id="L144" class="LineNr">144 </span><span class="Constant">    &lt;character-c-received&gt;</span>
+<span id="L145" class="LineNr">145 </span>    <span class="Delimiter">{</span>
+<span id="L146" class="LineNr">146 </span>      <span class="Comment"># newline? move to left rather than 0</span>
+<span id="L147" class="LineNr">147 </span>      newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
+<span id="L148" class="LineNr">148 </span>      <span class="muControl">break-unless</span> newline?
+<span id="L149" class="LineNr">149 </span>      <span class="Comment"># adjust cursor if necessary</span>
+<span id="L150" class="LineNr">150 </span>      <span class="Delimiter">{</span>
+<span id="L151" class="LineNr">151 </span>        at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
+<span id="L152" class="LineNr">152 </span>        <span class="muControl">break-unless</span> at-cursor-row?
+<span id="L153" class="LineNr">153 </span>        left-of-cursor?:bool <span class="Special">&lt;-</span> lesser-than column, cursor-column
+<span id="L154" class="LineNr">154 </span>        <span class="muControl">break-unless</span> left-of-cursor?
+<span id="L155" class="LineNr">155 </span>        cursor-column <span class="Special">&lt;-</span> copy column
+<span id="L156" class="LineNr">156 </span>        before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
+<span id="L157" class="LineNr">157 </span>      <span class="Delimiter">}</span>
+<span id="L158" class="LineNr">158 </span>      <span class="Comment"># clear rest of line in this window</span>
+<span id="L159" class="LineNr">159 </span>      <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
+<span id="L160" class="LineNr">160 </span>      <span class="Comment"># skip to next line</span>
+<span id="L161" class="LineNr">161 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
+<span id="L162" class="LineNr">162 </span>      column <span class="Special">&lt;-</span> copy left
+<span id="L163" class="LineNr">163 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
+<span id="L164" class="LineNr">164 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L165" class="LineNr">165 </span>      <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L166" class="LineNr">166 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
+<span id="L167" class="LineNr">167 </span>    <span class="Delimiter">}</span>
+<span id="L168" class="LineNr">168 </span>    <span class="Delimiter">{</span>
+<span id="L169" class="LineNr">169 </span>      <span class="Comment"># at right? wrap. even if there's only one more letter left; we need</span>
+<span id="L170" class="LineNr">170 </span>      <span class="Comment"># room for clicking on the cursor after it.</span>
+<span id="L171" class="LineNr">171 </span>      at-right?:bool <span class="Special">&lt;-</span> equal column, right
+<span id="L172" class="LineNr">172 </span>      <span class="muControl">break-unless</span> at-right?
+<span id="L173" class="LineNr">173 </span>      <span class="Comment"># print wrap icon</span>
+<span id="L174" class="LineNr">174 </span>      wrap-icon:char <span class="Special">&lt;-</span> copy <span class="Constant">8617/loop-back-to-left</span>
+<span id="L175" class="LineNr">175 </span>      print <a href='../081print.mu.html#L16'>screen</a>, wrap-icon, <span class="Constant">245/grey</span>
+<span id="L176" class="LineNr">176 </span>      column <span class="Special">&lt;-</span> copy left
+<span id="L177" class="LineNr">177 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
+<span id="L178" class="LineNr">178 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
+<span id="L179" class="LineNr">179 </span>      <span class="Comment"># don't increment curr</span>
+<span id="L180" class="LineNr">180 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
+<span id="L181" class="LineNr">181 </span>    <span class="Delimiter">}</span>
+<span id="L182" class="LineNr">182 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c, color
+<span id="L183" class="LineNr">183 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L184" class="LineNr">184 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L185" class="LineNr">185 </span>    column <span class="Special">&lt;-</span> add column,<span class="Constant"> 1</span>
+<span id="L186" class="LineNr">186 </span>   <span class="muControl"> loop</span>
+<span id="L187" class="LineNr">187 </span>  <span class="Delimiter">}</span>
+<span id="L188" class="LineNr">188 </span>  <span class="Comment"># save first character off-screen</span>
+<span id="L189" class="LineNr">189 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">bottom-of-screen:offset</span>, curr
+<span id="L190" class="LineNr">190 </span>  <span class="Comment"># is cursor to the right of the last line? move to end</span>
+<span id="L191" class="LineNr">191 </span>  <span class="Delimiter">{</span>
+<span id="L192" class="LineNr">192 </span>    at-cursor-row?:bool <span class="Special">&lt;-</span> equal row, cursor-row
+<span id="L193" class="LineNr">193 </span>    cursor-outside-line?:bool <span class="Special">&lt;-</span> lesser-or-equal column, cursor-column
+<span id="L194" class="LineNr">194 </span>    before-cursor-on-same-line?:bool <span class="Special">&lt;-</span> and at-cursor-row?, cursor-outside-line?
+<span id="L195" class="LineNr">195 </span>    above-cursor-row?:bool <span class="Special">&lt;-</span> lesser-than row, cursor-row
+<span id="L196" class="LineNr">196 </span>    before-cursor?:bool <span class="Special">&lt;-</span> or before-cursor-on-same-line?, above-cursor-row?
+<span id="L197" class="LineNr">197 </span>    <span class="muControl">break-unless</span> before-cursor?
+<span id="L198" class="LineNr">198 </span>    cursor-row <span class="Special">&lt;-</span> copy row
+<span id="L199" class="LineNr">199 </span>    cursor-column <span class="Special">&lt;-</span> copy column
+<span id="L200" class="LineNr">200 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L201" class="LineNr">201 </span>  <span class="Delimiter">}</span>
+<span id="L202" class="LineNr">202 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">bottom:offset</span>, row
+<span id="L203" class="LineNr">203 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
+<span id="L204" class="LineNr">204 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
+<span id="L205" class="LineNr">205 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
+<span id="L206" class="LineNr">206 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
+<span id="L207" class="LineNr">207 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
+<span id="L208" class="LineNr">208 </span> <span class="muControl"> return</span> row, left/column
+<span id="L209" class="LineNr">209 </span>]
+<span id="L210" class="LineNr">210 </span>
+<span id="L211" class="LineNr">211 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L211'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, row:num, column:num, left:num, right:num<span class="muRecipe"> -&gt; </span><a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
+<span id="L212" class="LineNr">212 </span>  <span class="Constant">local-scope</span>
+<span id="L213" class="LineNr">213 </span>  <span class="Constant">load-inputs</span>
+<span id="L214" class="LineNr">214 </span>  <span class="Comment"># if it's the real screen, use the optimized primitive</span>
+<span id="L215" class="LineNr">215 </span>  <span class="Delimiter">{</span>
+<span id="L216" class="LineNr">216 </span>    <span class="muControl">break-if</span> <a href='../081print.mu.html#L16'>screen</a>
+<span id="L217" class="LineNr">217 </span>    clear-display-from row, column, left, right
+<span id="L218" class="LineNr">218 </span>   <span class="muControl"> return</span>
+<span id="L219" class="LineNr">219 </span>  <span class="Delimiter">}</span>
+<span id="L220" class="LineNr">220 </span>  <span class="Comment"># if not, go the slower route</span>
+<span id="L221" class="LineNr">221 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
+<span id="L222" class="LineNr">222 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
+<span id="L223" class="LineNr">223 </span>  <a href='001-editor.mu.html#L226'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
+<span id="L224" class="LineNr">224 </span>]
+<span id="L225" class="LineNr">225 </span>
+<span id="L226" class="LineNr">226 </span><span class="muRecipe">def</span> <a href='001-editor.mu.html#L226'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, row:num, left:num, right:num<span class="muRecipe"> -&gt; </span><a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
+<span id="L227" class="LineNr">227 </span>  <span class="Constant">local-scope</span>
+<span id="L228" class="LineNr">228 </span>  <span class="Constant">load-inputs</span>
+<span id="L229" class="LineNr">229 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
+<span id="L230" class="LineNr">230 </span>  <span class="Comment"># if it's the real screen, use the optimized primitive</span>
+<span id="L231" class="LineNr">231 </span>  <span class="Delimiter">{</span>
+<span id="L232" class="LineNr">232 </span>    <span class="muControl">break-if</span> <a href='../081print.mu.html#L16'>screen</a>
+<span id="L233" class="LineNr">233 </span>    clear-display-from row, left, left, right
+<span id="L234" class="LineNr">234 </span>   <span class="muControl"> return</span>
+<span id="L235" class="LineNr">235 </span>  <span class="Delimiter">}</span>
+<span id="L236" class="LineNr">236 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, left
+<span id="L237" class="LineNr">237 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
+<span id="L238" class="LineNr">238 </span>  <span class="Delimiter">{</span>
+<span id="L239" class="LineNr">239 </span>    at-bottom-of-screen?:bool <span class="Special">&lt;-</span> greater-or-equal row, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L240" class="LineNr">240 </span>    <span class="muControl">break-if</span> at-bottom-of-screen?
+<span id="L241" class="LineNr">241 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, left
+<span id="L242" class="LineNr">242 </span>    <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
+<span id="L243" class="LineNr">243 </span>    row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
+<span id="L244" class="LineNr">244 </span>   <span class="muControl"> loop</span>
+<span id="L245" class="LineNr">245 </span>  <span class="Delimiter">}</span>
+<span id="L246" class="LineNr">246 </span>]
+<span id="L247" class="LineNr">247 </span>
+<span id="L248" class="LineNr">248 </span><span class="muScenario">scenario</span> editor-prints-multiple-lines [
+<span id="L249" class="LineNr">249 </span>  <span class="Constant">local-scope</span>
+<span id="L250" class="LineNr">250 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
+<span id="L251" class="LineNr">251 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
+<span id="L252" class="LineNr">252 </span><span class="Constant">def]</span>
+<span id="L253" class="LineNr">253 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L254" class="LineNr">254 </span>  run [
+<span id="L255" class="LineNr">255 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L256" class="LineNr">256 </span>  ]
+<span id="L257" class="LineNr">257 </span>  screen-should-contain [
+<span id="L258" class="LineNr">258 </span>   <span class="Constant"> .     .</span>
+<span id="L259" class="LineNr">259 </span>   <span class="Constant"> .abc  .</span>
+<span id="L260" class="LineNr">260 </span>   <span class="Constant"> .def  .</span>
+<span id="L261" class="LineNr">261 </span>   <span class="Constant"> .     .</span>
+<span id="L262" class="LineNr">262 </span>  ]
+<span id="L263" class="LineNr">263 </span>]
+<span id="L264" class="LineNr">264 </span>
+<span id="L265" class="LineNr">265 </span><span class="muScenario">scenario</span> editor-handles-offsets [
+<span id="L266" class="LineNr">266 </span>  <span class="Constant">local-scope</span>
+<span id="L267" class="LineNr">267 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
+<span id="L268" class="LineNr">268 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abc]</span>, <span class="Constant">1/left</span>, <span class="Constant">5/right</span>
+<span id="L269" class="LineNr">269 </span>  run [
+<span id="L270" class="LineNr">270 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L271" class="LineNr">271 </span>  ]
+<span id="L272" class="LineNr">272 </span>  screen-should-contain [
 <span id="L273" class="LineNr">273 </span>   <span class="Constant"> .     .</span>
-<span id="L274" class="LineNr">274 </span>  ]
-<span id="L275" class="LineNr">275 </span>]
-<span id="L276" class="LineNr">276 </span>
-<span id="L277" class="LineNr">277 </span><span class="muScenario">scenario</span> editor-prints-multiple-lines-at-offset [
-<span id="L278" class="LineNr">278 </span>  <span class="Constant">local-scope</span>
-<span id="L279" class="LineNr">279 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
-<span id="L280" class="LineNr">280 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
-<span id="L281" class="LineNr">281 </span><span class="Constant">def]</span>
-<span id="L282" class="LineNr">282 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">1/left</span>, <span class="Constant">5/right</span>
-<span id="L283" class="LineNr">283 </span>  run [
-<span id="L284" class="LineNr">284 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L285" class="LineNr">285 </span>  ]
-<span id="L286" class="LineNr">286 </span>  screen-should-contain [
-<span id="L287" class="LineNr">287 </span>   <span class="Constant"> .     .</span>
-<span id="L288" class="LineNr">288 </span>   <span class="Constant"> . abc .</span>
-<span id="L289" class="LineNr">289 </span>   <span class="Constant"> . def .</span>
-<span id="L290" class="LineNr">290 </span>   <span class="Constant"> .     .</span>
-<span id="L291" class="LineNr">291 </span>  ]
-<span id="L292" class="LineNr">292 </span>]
-<span id="L293" class="LineNr">293 </span>
-<span id="L294" class="LineNr">294 </span><span class="muScenario">scenario</span> editor-wraps-long-lines [
-<span id="L295" class="LineNr">295 </span>  <span class="Constant">local-scope</span>
-<span id="L296" class="LineNr">296 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
-<span id="L297" class="LineNr">297 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abc def]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L298" class="LineNr">298 </span>  run [
-<span id="L299" class="LineNr">299 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L300" class="LineNr">300 </span>  ]
-<span id="L301" class="LineNr">301 </span>  screen-should-contain [
-<span id="L302" class="LineNr">302 </span>   <span class="Constant"> .     .</span>
-<span id="L303" class="LineNr">303 </span>   <span class="Constant"> .abc ↩.</span>
-<span id="L304" class="LineNr">304 </span>   <span class="Constant"> .def  .</span>
-<span id="L305" class="LineNr">305 </span>   <span class="Constant"> .     .</span>
-<span id="L306" class="LineNr">306 </span>  ]
-<span id="L307" class="LineNr">307 </span>  screen-should-contain-in-color <span class="Constant">245/grey</span> [
-<span id="L308" class="LineNr">308 </span>   <span class="Constant"> .     .</span>
-<span id="L309" class="LineNr">309 </span>   <span class="Constant"> .    ↩.</span>
+<span id="L274" class="LineNr">274 </span>   <span class="Constant"> . abc .</span>
+<span id="L275" class="LineNr">275 </span>   <span class="Constant"> .     .</span>
+<span id="L276" class="LineNr">276 </span>  ]
+<span id="L277" class="LineNr">277 </span>]
+<span id="L278" class="LineNr">278 </span>
+<span id="L279" class="LineNr">279 </span><span class="muScenario">scenario</span> editor-prints-multiple-lines-at-offset [
+<span id="L280" class="LineNr">280 </span>  <span class="Constant">local-scope</span>
+<span id="L281" class="LineNr">281 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
+<span id="L282" class="LineNr">282 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
+<span id="L283" class="LineNr">283 </span><span class="Constant">def]</span>
+<span id="L284" class="LineNr">284 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">1/left</span>, <span class="Constant">5/right</span>
+<span id="L285" class="LineNr">285 </span>  run [
+<span id="L286" class="LineNr">286 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L287" class="LineNr">287 </span>  ]
+<span id="L288" class="LineNr">288 </span>  screen-should-contain [
+<span id="L289" class="LineNr">289 </span>   <span class="Constant"> .     .</span>
+<span id="L290" class="LineNr">290 </span>   <span class="Constant"> . abc .</span>
+<span id="L291" class="LineNr">291 </span>   <span class="Constant"> . def .</span>
+<span id="L292" class="LineNr">292 </span>   <span class="Constant"> .     .</span>
+<span id="L293" class="LineNr">293 </span>  ]
+<span id="L294" class="LineNr">294 </span>]
+<span id="L295" class="LineNr">295 </span>
+<span id="L296" class="LineNr">296 </span><span class="muScenario">scenario</span> editor-wraps-long-lines [
+<span id="L297" class="LineNr">297 </span>  <span class="Constant">local-scope</span>
+<span id="L298" class="LineNr">298 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
+<span id="L299" class="LineNr">299 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abc def]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L300" class="LineNr">300 </span>  run [
+<span id="L301" class="LineNr">301 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L302" class="LineNr">302 </span>  ]
+<span id="L303" class="LineNr">303 </span>  screen-should-contain [
+<span id="L304" class="LineNr">304 </span>   <span class="Constant"> .     .</span>
+<span id="L305" class="LineNr">305 </span>   <span class="Constant"> .abc ↩.</span>
+<span id="L306" class="LineNr">306 </span>   <span class="Constant"> .def  .</span>
+<span id="L307" class="LineNr">307 </span>   <span class="Constant"> .     .</span>
+<span id="L308" class="LineNr">308 </span>  ]
+<span id="L309" class="LineNr">309 </span>  screen-should-contain-in-color <span class="Constant">245/grey</span> [
 <span id="L310" class="LineNr">310 </span>   <span class="Constant"> .     .</span>
-<span id="L311" class="LineNr">311 </span>   <span class="Constant"> .     .</span>
-<span id="L312" class="LineNr">312 </span>  ]
-<span id="L313" class="LineNr">313 </span>]
-<span id="L314" class="LineNr">314 </span>
-<span id="L315" class="LineNr">315 </span><span class="muScenario">scenario</span> editor-wraps-barely-long-lines [
-<span id="L316" class="LineNr">316 </span>  <span class="Constant">local-scope</span>
-<span id="L317" class="LineNr">317 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
-<span id="L318" class="LineNr">318 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abcde]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L319" class="LineNr">319 </span>  run [
-<span id="L320" class="LineNr">320 </span>    <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L321" class="LineNr">321 </span>  ]
-<span id="L322" class="LineNr">322 </span>  <span class="Comment"># still wrap, even though the line would fit. We need room to click on the</span>
-<span id="L323" class="LineNr">323 </span>  <span class="Comment"># end of the line</span>
-<span id="L324" class="LineNr">324 </span>  screen-should-contain [
-<span id="L325" class="LineNr">325 </span>   <span class="Constant"> .     .</span>
-<span id="L326" class="LineNr">326 </span><span class="Constant">    .abcd↩.</span>
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-<span id="L328" class="LineNr">328 </span>   <span class="Constant"> .     .</span>
-<span id="L329" class="LineNr">329 </span>  ]
-<span id="L330" class="LineNr">330 </span>  screen-should-contain-in-color <span class="Constant">245/grey</span> [
-<span id="L331" class="LineNr">331 </span>   <span class="Constant"> .     .</span>
-<span id="L332" class="LineNr">332 </span>   <span class="Constant"> .    ↩.</span>
+<span id="L311" class="LineNr">311 </span>   <span class="Constant"> .    ↩.</span>
+<span id="L312" class="LineNr">312 </span>   <span class="Constant"> .     .</span>
+<span id="L313" class="LineNr">313 </span>   <span class="Constant"> .     .</span>
+<span id="L314" class="LineNr">314 </span>  ]
+<span id="L315" class="LineNr">315 </span>]
+<span id="L316" class="LineNr">316 </span>
+<span id="L317" class="LineNr">317 </span><span class="muScenario">scenario</span> editor-wraps-barely-long-lines [
+<span id="L318" class="LineNr">318 </span>  <span class="Constant">local-scope</span>
+<span id="L319" class="LineNr">319 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">5/height</span>
+<span id="L320" class="LineNr">320 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abcde]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L321" class="LineNr">321 </span>  run [
+<span id="L322" class="LineNr">322 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L323" class="LineNr">323 </span>  ]
+<span id="L324" class="LineNr">324 </span>  <span class="Comment"># still wrap, even though the line would fit. We need room to click on the</span>
+<span id="L325" class="LineNr">325 </span>  <span class="Comment"># end of the line</span>
+<span id="L326" class="LineNr">326 </span>  screen-should-contain [
+<span id="L327" class="LineNr">327 </span>   <span class="Constant"> .     .</span>
+<span id="L328" class="LineNr">328 </span><span class="Constant">    .abcd↩.</span>
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+<span id="L330" class="LineNr">330 </span>   <span class="Constant"> .     .</span>
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+<span id="L422" class="LineNr">422 </span>  <span class="Delimiter">{</span>
+<span id="L423" class="LineNr">423 </span>    <span class="muControl">break-unless</span> color-is-white?
+<span id="L424" class="LineNr">424 </span>    starting-assignment?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">60/&lt;</span>
+<span id="L425" class="LineNr">425 </span>    <span class="muControl">break-unless</span> starting-assignment?
+<span id="L426" class="LineNr">426 </span>   <span class="muControl"> return</span> <span class="Constant">1/red</span>
+<span id="L427" class="LineNr">427 </span>  <span class="Delimiter">}</span>
+<span id="L428" class="LineNr">428 </span>  <span class="Comment"># if color is red and next character is space, switch color to white</span>
+<span id="L429" class="LineNr">429 </span>  <span class="Delimiter">{</span>
+<span id="L430" class="LineNr">430 </span>    color-is-red?:bool <span class="Special">&lt;-</span> equal color, <span class="Constant">1/red</span>
+<span id="L431" class="LineNr">431 </span>    <span class="muControl">break-unless</span> color-is-red?
+<span id="L432" class="LineNr">432 </span>    ending-assignment?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">32/space</span>
+<span id="L433" class="LineNr">433 </span>    <span class="muControl">break-unless</span> ending-assignment?
+<span id="L434" class="LineNr">434 </span>   <span class="muControl"> return</span> <span class="Constant">7/white</span>
+<span id="L435" class="LineNr">435 </span>  <span class="Delimiter">}</span>
+<span id="L436" class="LineNr">436 </span>  <span class="Comment"># otherwise no change</span>
+<span id="L437" class="LineNr">437 </span> <span class="muControl"> return</span> color
+<span id="L438" class="LineNr">438 </span>]
+<span id="L439" class="LineNr">439 </span>
+<span id="L440" class="LineNr">440 </span><span class="muScenario">scenario</span> render-colors-assignment [
+<span id="L441" class="LineNr">441 </span>  <span class="Constant">local-scope</span>
+<span id="L442" class="LineNr">442 </span>  assume-screen <span class="Constant">8/width</span>, <span class="Constant">5/height</span>
+<span id="L443" class="LineNr">443 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
+<span id="L444" class="LineNr">444 </span><span class="Constant">d &lt;- e</span>
+<span id="L445" class="LineNr">445 </span><span class="Constant">f]</span>
+<span id="L446" class="LineNr">446 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">8/right</span>
+<span id="L447" class="LineNr">447 </span>  run [
+<span id="L448" class="LineNr">448 </span>    <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L449" class="LineNr">449 </span>  ]
+<span id="L450" class="LineNr">450 </span>  screen-should-contain [
+<span id="L451" class="LineNr">451 </span>   <span class="Constant"> .        .</span>
+<span id="L452" class="LineNr">452 </span>   <span class="Constant"> .abc     .</span>
+<span id="L453" class="LineNr">453 </span>   <span class="Constant"> .d &lt;- e  .</span>
+<span id="L454" class="LineNr">454 </span>   <span class="Constant"> .f       .</span>
+<span id="L455" class="LineNr">455 </span>   <span class="Constant"> .        .</span>
+<span id="L456" class="LineNr">456 </span>  ]
+<span id="L457" class="LineNr">457 </span>  screen-should-contain-in-color <span class="Constant">1/red</span>, [
+<span id="L458" class="LineNr">458 </span>   <span class="Constant"> .        .</span>
 <span id="L459" class="LineNr">459 </span>   <span class="Constant"> .        .</span>
-<span id="L460" class="LineNr">460 </span>   <span class="Constant"> .        .</span>
-<span id="L461" class="LineNr">461 </span>  ]
-<span id="L462" class="LineNr">462 </span>]
+<span id="L460" class="LineNr">460 </span>   <span class="Constant"> .  &lt;-    .</span>
+<span id="L461" class="LineNr">461 </span>   <span class="Constant"> .        .</span>
+<span id="L462" class="LineNr">462 </span>   <span class="Constant"> .        .</span>
+<span id="L463" class="LineNr">463 </span>  ]
+<span id="L464" class="LineNr">464 </span>]
 </pre>
 </body>
 </html>
diff --git a/html/edit/002-typing.mu.html b/html/edit/002-typing.mu.html
index a0cb8c06..f33cf545 100644
--- a/html/edit/002-typing.mu.html
+++ b/html/edit/002-typing.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.Delimiter { color: #800080; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
-.Delimiter { color: #800080; }
+.muData { color: #ffff00; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -68,10 +68,10 @@ if ('onhashchange' in window) {
 <span id="L6" class="LineNr">   6 </span>  <span class="Constant">local-scope</span>
 <span id="L7" class="LineNr">   7 </span>  <span class="Constant">load-inputs</span>
 <span id="L8" class="LineNr">   8 </span>  open-console
-<span id="L9" class="LineNr">   9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a> <span class="Constant">0/screen</span>  <span class="Comment"># non-scrolling app</span>
+<span id="L9" class="LineNr">   9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a><span class="Constant"> null/screen</span>  <span class="Comment"># non-scrolling app</span>
 <span id="L10" class="LineNr">  10 </span>  editor:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> text, <span class="Constant">5/left</span>, <span class="Constant">45/right</span>
-<span id="L11" class="LineNr">  11 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <span class="Constant">0/screen</span>, editor
-<span id="L12" class="LineNr">  12 </span>  <a href='002-typing.mu.html#L16'>editor-event-loop</a> <span class="Constant">0/screen</span>, <span class="Constant">0/console</span>, editor
+<span id="L11" class="LineNr">  11 </span>  <a href='002-typing.mu.html#L265'>editor-render</a><span class="Constant"> null/screen,</span> editor
+<span id="L12" class="LineNr">  12 </span>  <a href='002-typing.mu.html#L16'>editor-event-loop</a><span class="Constant"> null/screen, null/console,</span> editor
 <span id="L13" class="LineNr">  13 </span>  close-console
 <span id="L14" class="LineNr">  14 </span>]
 <span id="L15" class="LineNr">  15 </span>
@@ -112,23 +112,23 @@ if ('onhashchange' in window) {
 <span id="L50" class="LineNr">  50 </span><span class="muRecipe">def</span> move-cursor editor:&amp;:editor, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, t:<a href='../084console.mu.html#L12'>touch-event</a><span class="muRecipe"> -&gt; </span>in-focus?:bool, editor:&amp;:editor [
 <span id="L51" class="LineNr">  51 </span>  <span class="Constant">local-scope</span>
 <span id="L52" class="LineNr">  52 </span>  <span class="Constant">load-inputs</span>
-<span id="L53" class="LineNr">  53 </span>  <span class="muControl">return-unless</span> editor, <span class="Constant">0/false</span>
+<span id="L53" class="LineNr">  53 </span>  <span class="muControl">return-unless</span> editor,<span class="Constant"> false</span>
 <span id="L54" class="LineNr">  54 </span>  click-row:num <span class="Special">&lt;-</span> get t, <span class="Constant">row:offset</span>
-<span id="L55" class="LineNr">  55 </span>  <span class="muControl">return-unless</span> click-row, <span class="Constant">0/false</span>  <span class="Comment"># ignore clicks on 'menu'</span>
+<span id="L55" class="LineNr">  55 </span>  <span class="muControl">return-unless</span> click-row,<span class="Constant"> false</span>  <span class="Comment"># ignore clicks on 'menu'</span>
 <span id="L56" class="LineNr">  56 </span>  click-column:num <span class="Special">&lt;-</span> get t, <span class="Constant">column:offset</span>
 <span id="L57" class="LineNr">  57 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
 <span id="L58" class="LineNr">  58 </span>  too-far-left?:bool <span class="Special">&lt;-</span> lesser-than click-column, left
-<span id="L59" class="LineNr">  59 </span>  <span class="muControl">return-if</span> too-far-left?, <span class="Constant">0/false</span>
+<span id="L59" class="LineNr">  59 </span>  <span class="muControl">return-if</span> too-far-left?,<span class="Constant"> false</span>
 <span id="L60" class="LineNr">  60 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
 <span id="L61" class="LineNr">  61 </span>  too-far-right?:bool <span class="Special">&lt;-</span> greater-than click-column, right
-<span id="L62" class="LineNr">  62 </span>  <span class="muControl">return-if</span> too-far-right?, <span class="Constant">0/false</span>
+<span id="L62" class="LineNr">  62 </span>  <span class="muControl">return-if</span> too-far-right?,<span class="Constant"> false</span>
 <span id="L63" class="LineNr">  63 </span>  <span class="Comment"># position cursor</span>
 <span id="L64" class="LineNr">  64 </span><span class="Constant">  &lt;begin-move-cursor&gt;</span>
 <span id="L65" class="LineNr">  65 </span>  editor <span class="Special">&lt;-</span> <a href='002-typing.mu.html#L75'>snap-cursor</a> editor, <a href='../081print.mu.html#L16'>screen</a>, click-row, click-column
 <span id="L66" class="LineNr">  66 </span>  undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
 <span id="L67" class="LineNr">  67 </span><span class="Constant">  &lt;end-move-cursor&gt;</span>
 <span id="L68" class="LineNr">  68 </span>  <span class="Comment"># gain focus</span>
-<span id="L69" class="LineNr">  69 </span> <span class="muControl"> return</span> <span class="Constant">1/true</span>
+<span id="L69" class="LineNr">  69 </span> <span class="muControl"> return</span><span class="Constant"> true</span>
 <span id="L70" class="LineNr">  70 </span>]
 <span id="L71" class="LineNr">  71 </span>
 <span id="L72" class="LineNr">  72 </span><span class="Comment"># Variant of 'render' that only moves the cursor (coordinates and</span>
@@ -143,8 +143,8 @@ if ('onhashchange' in window) {
 <span id="L81" class="LineNr">  81 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L82" class="LineNr">  82 </span>  <span class="Comment"># count newlines until screen row</span>
 <span id="L83" class="LineNr">  83 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L84" class="LineNr">  84 </span>  <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
-<span id="L85" class="LineNr">  85 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L84" class="LineNr">  84 </span>  <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
+<span id="L85" class="LineNr">  85 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L86" class="LineNr">  86 </span>  row:num <span class="Special">&lt;-</span> copy <span class="Constant">1/top</span>
 <span id="L87" class="LineNr">  87 </span>  column:num <span class="Special">&lt;-</span> copy left
 <span id="L88" class="LineNr">  88 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, target-row
@@ -165,7 +165,7 @@ if ('onhashchange' in window) {
 <span id="L103" class="LineNr"> 103 </span>      <span class="muControl">break-unless</span> at-cursor-row?
 <span id="L104" class="LineNr"> 104 </span>      at-cursor?:bool <span class="Special">&lt;-</span> equal column, cursor-column
 <span id="L105" class="LineNr"> 105 </span>      <span class="muControl">break-unless</span> at-cursor?
-<span id="L106" class="LineNr"> 106 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L106" class="LineNr"> 106 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L107" class="LineNr"> 107 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L108" class="LineNr"> 108 </span>    <span class="Delimiter">}</span>
 <span id="L109" class="LineNr"> 109 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
@@ -181,14 +181,14 @@ if ('onhashchange' in window) {
 <span id="L119" class="LineNr"> 119 </span>        <span class="muControl">break-unless</span> left-of-cursor?
 <span id="L120" class="LineNr"> 120 </span>        cursor-column <span class="Special">&lt;-</span> copy column
 <span id="L121" class="LineNr"> 121 </span>        *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L122" class="LineNr"> 122 </span>        before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L122" class="LineNr"> 122 </span>        before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L123" class="LineNr"> 123 </span>        *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L124" class="LineNr"> 124 </span>      <span class="Delimiter">}</span>
 <span id="L125" class="LineNr"> 125 </span>      <span class="Comment"># skip to next line</span>
 <span id="L126" class="LineNr"> 126 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
 <span id="L127" class="LineNr"> 127 </span>      column <span class="Special">&lt;-</span> copy left
-<span id="L128" class="LineNr"> 128 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L129" class="LineNr"> 129 </span>      <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L128" class="LineNr"> 128 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L129" class="LineNr"> 129 </span>      <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L130" class="LineNr"> 130 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
 <span id="L131" class="LineNr"> 131 </span>    <span class="Delimiter">}</span>
 <span id="L132" class="LineNr"> 132 </span>    <span class="Delimiter">{</span>
@@ -201,8 +201,8 @@ if ('onhashchange' in window) {
 <span id="L139" class="LineNr"> 139 </span>      <span class="Comment"># don't increment curr/prev</span>
 <span id="L140" class="LineNr"> 140 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
 <span id="L141" class="LineNr"> 141 </span>    <span class="Delimiter">}</span>
-<span id="L142" class="LineNr"> 142 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L143" class="LineNr"> 143 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L142" class="LineNr"> 142 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L143" class="LineNr"> 143 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L144" class="LineNr"> 144 </span>    column <span class="Special">&lt;-</span> add column,<span class="Constant"> 1</span>
 <span id="L145" class="LineNr"> 145 </span>   <span class="muControl"> loop</span>
 <span id="L146" class="LineNr"> 146 </span>  <span class="Delimiter">}</span>
@@ -218,7 +218,7 @@ if ('onhashchange' in window) {
 <span id="L156" class="LineNr"> 156 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
 <span id="L157" class="LineNr"> 157 </span>    cursor-column <span class="Special">&lt;-</span> copy column
 <span id="L158" class="LineNr"> 158 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L159" class="LineNr"> 159 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L159" class="LineNr"> 159 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L160" class="LineNr"> 160 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L161" class="LineNr"> 161 </span>  <span class="Delimiter">}</span>
 <span id="L162" class="LineNr"> 162 </span>]
@@ -228,7 +228,7 @@ if ('onhashchange' in window) {
 <span id="L166" class="LineNr"> 166 </span><span class="muRecipe">def</span> <a href='002-typing.mu.html#L166'>handle-keyboard-event</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor, e:<a href='../084console.mu.html#L4'>event</a><span class="muRecipe"> -&gt; </span>go-render?:bool, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor [
 <span id="L167" class="LineNr"> 167 </span>  <span class="Constant">local-scope</span>
 <span id="L168" class="LineNr"> 168 </span>  <span class="Constant">load-inputs</span>
-<span id="L169" class="LineNr"> 169 </span>  <span class="muControl">return-unless</span> editor, <span class="Constant">0/don't-render</span>
+<span id="L169" class="LineNr"> 169 </span>  <span class="muControl">return-unless</span> editor,<span class="Constant"> false/don't-render</span>
 <span id="L170" class="LineNr"> 170 </span>  <a href='../081print.mu.html#L768'>screen-width</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L768'>screen-width</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L171" class="LineNr"> 171 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L172" class="LineNr"> 172 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
@@ -247,7 +247,7 @@ if ('onhashchange' in window) {
 <span id="L185" class="LineNr"> 185 </span><span class="Constant">    <a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span>
 <span id="L186" class="LineNr"> 186 </span>    <span class="Comment"># ignore any other special characters</span>
 <span id="L187" class="LineNr"> 187 </span>    regular-character?:bool <span class="Special">&lt;-</span> greater-or-equal c, <span class="Constant">32/space</span>
-<span id="L188" class="LineNr"> 188 </span>    <span class="muControl">return-unless</span> regular-character?, <span class="Constant">0/don't-render</span>
+<span id="L188" class="LineNr"> 188 </span>    <span class="muControl">return-unless</span> regular-character?,<span class="Constant"> false/don't-render</span>
 <span id="L189" class="LineNr"> 189 </span>    <span class="Comment"># otherwise type it in</span>
 <span id="L190" class="LineNr"> 190 </span><span class="Constant">    &lt;begin-insert-character&gt;</span>
 <span id="L191" class="LineNr"> 191 </span>    go-render? <span class="Special">&lt;-</span> <a href='002-typing.mu.html#L203'>insert-at-cursor</a> editor, c, <a href='../081print.mu.html#L16'>screen</a>
@@ -259,7 +259,7 @@ if ('onhashchange' in window) {
 <span id="L197" class="LineNr"> 197 </span>  assert is-keycode?, <span class="Constant">[event was of unknown type; neither keyboard nor mouse]</span>
 <span id="L198" class="LineNr"> 198 </span>  <span class="Comment"># handlers for each special key will go here</span>
 <span id="L199" class="LineNr"> 199 </span><span class="Constant">  <a href='002-typing.mu.html#L199'>&lt;handle-special-key&gt;</a></span>
-<span id="L200" class="LineNr"> 200 </span> <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L200" class="LineNr"> 200 </span> <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L201" class="LineNr"> 201 </span>]
 <span id="L202" class="LineNr"> 202 </span>
 <span id="L203" class="LineNr"> 203 </span><span class="muRecipe">def</span> <a href='002-typing.mu.html#L203'>insert-at-cursor</a> editor:&amp;:editor, c:char, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a><span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
@@ -267,7 +267,7 @@ if ('onhashchange' in window) {
 <span id="L205" class="LineNr"> 205 </span>  <span class="Constant">load-inputs</span>
 <span id="L206" class="LineNr"> 206 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L207" class="LineNr"> 207 </span>  insert c, before-cursor
-<span id="L208" class="LineNr"> 208 </span>  before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L208" class="LineNr"> 208 </span>  before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L209" class="LineNr"> 209 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L210" class="LineNr"> 210 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L211" class="LineNr"> 211 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
@@ -282,10 +282,10 @@ if ('onhashchange' in window) {
 <span id="L220" class="LineNr"> 220 </span>  <span class="Comment"># but mostly we'll just move the cursor right</span>
 <span id="L221" class="LineNr"> 221 </span>  cursor-column <span class="Special">&lt;-</span> add cursor-column,<span class="Constant"> 1</span>
 <span id="L222" class="LineNr"> 222 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L223" class="LineNr"> 223 </span>  <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L223" class="LineNr"> 223 </span>  <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L224" class="LineNr"> 224 </span>  <span class="Delimiter">{</span>
 <span id="L225" class="LineNr"> 225 </span>    <span class="Comment"># at end of all text? no need to scroll? just print the character and leave</span>
-<span id="L226" class="LineNr"> 226 </span>    at-end?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L25'>next</a>, <span class="Constant">0/null</span>
+<span id="L226" class="LineNr"> 226 </span>    at-end?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L31'>next</a>,<span class="Constant"> null</span>
 <span id="L227" class="LineNr"> 227 </span>    <span class="muControl">break-unless</span> at-end?
 <span id="L228" class="LineNr"> 228 </span>    bottom:num <span class="Special">&lt;-</span> subtract <a href='../081print.mu.html#L782'>screen-height</a>,<span class="Constant"> 1</span>
 <span id="L229" class="LineNr"> 229 </span>    at-bottom?:bool <span class="Special">&lt;-</span> equal save-row, bottom
@@ -294,11 +294,11 @@ if ('onhashchange' in window) {
 <span id="L232" class="LineNr"> 232 </span>    <span class="muControl">break-if</span> overflow?
 <span id="L233" class="LineNr"> 233 </span>    move-cursor <a href='../081print.mu.html#L16'>screen</a>, save-row, save-column
 <span id="L234" class="LineNr"> 234 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c
-<span id="L235" class="LineNr"> 235 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L235" class="LineNr"> 235 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L236" class="LineNr"> 236 </span>  <span class="Delimiter">}</span>
 <span id="L237" class="LineNr"> 237 </span>  <span class="Delimiter">{</span>
 <span id="L238" class="LineNr"> 238 </span>    <span class="Comment"># not at right margin? print the character and rest of line</span>
-<span id="L239" class="LineNr"> 239 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L239" class="LineNr"> 239 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L240" class="LineNr"> 240 </span>    at-right?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, <a href='../081print.mu.html#L768'>screen-width</a>
 <span id="L241" class="LineNr"> 241 </span>    <span class="muControl">break-if</span> at-right?
 <span id="L242" class="LineNr"> 242 </span>    curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy before-cursor
@@ -307,7 +307,7 @@ if ('onhashchange' in window) {
 <span id="L245" class="LineNr"> 245 </span>    <span class="Delimiter">{</span>
 <span id="L246" class="LineNr"> 246 </span>      <span class="Comment"># hit right margin? give up and let caller render</span>
 <span id="L247" class="LineNr"> 247 </span>      at-right?:bool <span class="Special">&lt;-</span> greater-than curr-column, right
-<span id="L248" class="LineNr"> 248 </span>      <span class="muControl">return-if</span> at-right?, <span class="Constant">1/go-render</span>
+<span id="L248" class="LineNr"> 248 </span>      <span class="muControl">return-if</span> at-right?,<span class="Constant"> true/go-render</span>
 <span id="L249" class="LineNr"> 249 </span>      <span class="muControl">break-unless</span> curr
 <span id="L250" class="LineNr"> 250 </span>      <span class="Comment"># newline? done.</span>
 <span id="L251" class="LineNr"> 251 </span>      currc:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
@@ -315,12 +315,12 @@ if ('onhashchange' in window) {
 <span id="L253" class="LineNr"> 253 </span>      <span class="muControl">break-if</span> at-newline?
 <span id="L254" class="LineNr"> 254 </span>      print <a href='../081print.mu.html#L16'>screen</a>, currc
 <span id="L255" class="LineNr"> 255 </span>      curr-column <span class="Special">&lt;-</span> add curr-column,<span class="Constant"> 1</span>
-<span id="L256" class="LineNr"> 256 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L256" class="LineNr"> 256 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L257" class="LineNr"> 257 </span>     <span class="muControl"> loop</span>
 <span id="L258" class="LineNr"> 258 </span>    <span class="Delimiter">}</span>
-<span id="L259" class="LineNr"> 259 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L259" class="LineNr"> 259 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L260" class="LineNr"> 260 </span>  <span class="Delimiter">}</span>
-<span id="L261" class="LineNr"> 261 </span> <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L261" class="LineNr"> 261 </span> <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L262" class="LineNr"> 262 </span>]
 <span id="L263" class="LineNr"> 263 </span>
 <span id="L264" class="LineNr"> 264 </span><span class="Comment"># helper for tests</span>
@@ -330,10 +330,10 @@ if ('onhashchange' in window) {
 <span id="L268" class="LineNr"> 268 </span>  old-top-idx:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L509'>save-top-idx</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L269" class="LineNr"> 269 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
 <span id="L270" class="LineNr"> 270 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
-<span id="L271" class="LineNr"> 271 </span>  row:num, column:num <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L107'>render</a> <a href='../081print.mu.html#L16'>screen</a>, editor
+<span id="L271" class="LineNr"> 271 </span>  row:num, column:num <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L109'>render</a> <a href='../081print.mu.html#L16'>screen</a>, editor
 <span id="L272" class="LineNr"> 272 </span>  <a href='002-typing.mu.html#L1114'>draw-horizontal</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right, <span class="Constant">9480/horizontal-dotted</span>
 <span id="L273" class="LineNr"> 273 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L274" class="LineNr"> 274 </span>  <a href='001-editor.mu.html#L209'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
+<span id="L274" class="LineNr"> 274 </span>  <a href='001-editor.mu.html#L211'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
 <span id="L275" class="LineNr"> 275 </span>  <a href='../081print.mu.html#L515'>assert-no-scroll</a> <a href='../081print.mu.html#L16'>screen</a>, old-top-idx
 <span id="L276" class="LineNr"> 276 </span>]
 <span id="L277" class="LineNr"> 277 </span>
@@ -761,16 +761,16 @@ if ('onhashchange' in window) {
 <span id="L699" class="LineNr"> 699 </span>    before-wrap-column:num <span class="Special">&lt;-</span> subtract wrap-column,<span class="Constant"> 1</span>
 <span id="L700" class="LineNr"> 700 </span>    at-wrap?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, wrap-column
 <span id="L701" class="LineNr"> 701 </span>    just-before-wrap?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, before-wrap-column
-<span id="L702" class="LineNr"> 702 </span>    <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L702" class="LineNr"> 702 </span>    <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L703" class="LineNr"> 703 </span>    <span class="Comment"># at end of line? next == 0 || next.value == 10/newline</span>
-<span id="L704" class="LineNr"> 704 </span>    at-end-of-line?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L25'>next</a>,<span class="Constant"> 0</span>
+<span id="L704" class="LineNr"> 704 </span>    at-end-of-line?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L31'>next</a>,<span class="Constant"> null</span>
 <span id="L705" class="LineNr"> 705 </span>    <span class="Delimiter">{</span>
 <span id="L706" class="LineNr"> 706 </span>      <span class="muControl">break-if</span> at-end-of-line?
 <span id="L707" class="LineNr"> 707 </span>      next-character:char <span class="Special">&lt;-</span> get *next, <span class="Constant">value:offset</span>
 <span id="L708" class="LineNr"> 708 </span>      at-end-of-line? <span class="Special">&lt;-</span> equal next-character, <span class="Constant">10/newline</span>
 <span id="L709" class="LineNr"> 709 </span>    <span class="Delimiter">}</span>
 <span id="L710" class="LineNr"> 710 </span>    <span class="Comment"># break unless ((eol? and at-wrap?) or (~eol? and just-before-wrap?))</span>
-<span id="L711" class="LineNr"> 711 </span>    move-cursor-to-next-line?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L711" class="LineNr"> 711 </span>    move-cursor-to-next-line?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L712" class="LineNr"> 712 </span>    <span class="Delimiter">{</span>
 <span id="L713" class="LineNr"> 713 </span>      <span class="muControl">break-if</span> at-end-of-line?
 <span id="L714" class="LineNr"> 714 </span>      move-cursor-to-next-line? <span class="Special">&lt;-</span> copy just-before-wrap?
@@ -797,7 +797,7 @@ if ('onhashchange' in window) {
 <span id="L735" class="LineNr"> 735 </span>      <span class="muControl">break-unless</span> below-screen?
 <span id="L736" class="LineNr"> 736 </span><span class="Constant">      &lt;scroll-down&gt;</span>
 <span id="L737" class="LineNr"> 737 </span>    <span class="Delimiter">}</span>
-<span id="L738" class="LineNr"> 738 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L738" class="LineNr"> 738 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L739" class="LineNr"> 739 </span>  <span class="Delimiter">}</span>
 <span id="L740" class="LineNr"> 740 </span>]
 <span id="L741" class="LineNr"> 741 </span>
@@ -891,7 +891,7 @@ if ('onhashchange' in window) {
 <span id="L829" class="LineNr"> 829 </span>]
 <span id="L830" class="LineNr"> 830 </span>
 <span id="L831" class="LineNr"> 831 </span><span class="muRecipe">after</span> <span class="Constant"><a href='001-editor.mu.html#L69'>&lt;editor-initialization&gt;</a></span> [
-<span id="L832" class="LineNr"> 832 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">indent?:offset</span>, <span class="Constant">1/true</span>
+<span id="L832" class="LineNr"> 832 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">indent?:offset</span>,<span class="Constant"> true</span>
 <span id="L833" class="LineNr"> 833 </span>]
 <span id="L834" class="LineNr"> 834 </span>
 <span id="L835" class="LineNr"> 835 </span><span class="muScenario">scenario</span> editor-moves-cursor-down-after-inserting-newline [
@@ -921,7 +921,7 @@ if ('onhashchange' in window) {
 <span id="L859" class="LineNr"> 859 </span><span class="Constant">    <a href='002-typing.mu.html#L859'>&lt;begin-insert-enter&gt;</a></span>
 <span id="L860" class="LineNr"> 860 </span>    <a href='002-typing.mu.html#L866'>insert-new-line-and-indent</a> editor, <a href='../081print.mu.html#L16'>screen</a>
 <span id="L861" class="LineNr"> 861 </span><span class="Constant">    <a href='002-typing.mu.html#L861'>&lt;end-insert-enter&gt;</a></span>
-<span id="L862" class="LineNr"> 862 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L862" class="LineNr"> 862 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L863" class="LineNr"> 863 </span>  <span class="Delimiter">}</span>
 <span id="L864" class="LineNr"> 864 </span>]
 <span id="L865" class="LineNr"> 865 </span>
@@ -947,19 +947,19 @@ if ('onhashchange' in window) {
 <span id="L885" class="LineNr"> 885 </span>  <span class="Delimiter">{</span>
 <span id="L886" class="LineNr"> 886 </span>    below-screen?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-row, <a href='../081print.mu.html#L782'>screen-height</a>  <span class="Comment"># must be equal, never greater</span>
 <span id="L887" class="LineNr"> 887 </span>    <span class="muControl">break-unless</span> below-screen?
-<span id="L888" class="LineNr"> 888 </span><span class="Constant">    &lt;scroll-down&gt;</span>
+<span id="L888" class="LineNr"> 888 </span><span class="Constant">    <a href='002-typing.mu.html#L888'>&lt;scroll-down2&gt;</a></span>
 <span id="L889" class="LineNr"> 889 </span>    cursor-row <span class="Special">&lt;-</span> subtract cursor-row,<span class="Constant"> 1</span>  <span class="Comment"># bring back into screen range</span>
 <span id="L890" class="LineNr"> 890 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
 <span id="L891" class="LineNr"> 891 </span>  <span class="Delimiter">}</span>
 <span id="L892" class="LineNr"> 892 </span>  <span class="Comment"># insert newline</span>
 <span id="L893" class="LineNr"> 893 </span>  insert <span class="Constant">10/newline</span>, before-cursor
-<span id="L894" class="LineNr"> 894 </span>  before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L894" class="LineNr"> 894 </span>  before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L895" class="LineNr"> 895 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L896" class="LineNr"> 896 </span>  <span class="Comment"># indent if necessary</span>
 <span id="L897" class="LineNr"> 897 </span>  indent?:bool <span class="Special">&lt;-</span> get *editor, <span class="Constant">indent?:offset</span>
 <span id="L898" class="LineNr"> 898 </span>  <span class="muControl">return-unless</span> indent?
 <span id="L899" class="LineNr"> 899 </span>  d:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L900" class="LineNr"> 900 </span>  end-of-previous-line:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
+<span id="L900" class="LineNr"> 900 </span>  end-of-previous-line:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
 <span id="L901" class="LineNr"> 901 </span>  indent:num <span class="Special">&lt;-</span> <a href='002-typing.mu.html#L932'>line-indent</a> end-of-previous-line, d
 <span id="L902" class="LineNr"> 902 </span>  i:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
 <span id="L903" class="LineNr"> 903 </span>  <span class="Delimiter">{</span>
@@ -977,16 +977,16 @@ if ('onhashchange' in window) {
 <span id="L915" class="LineNr"> 915 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
 <span id="L916" class="LineNr"> 916 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L917" class="LineNr"> 917 </span>  cursor-at-left?:bool <span class="Special">&lt;-</span> equal cursor-column, left
-<span id="L918" class="LineNr"> 918 </span>  <span class="muControl">return-unless</span> cursor-at-left?, <span class="Constant">0/false</span>
+<span id="L918" class="LineNr"> 918 </span>  <span class="muControl">return-unless</span> cursor-at-left?,<span class="Constant"> false</span>
 <span id="L919" class="LineNr"> 919 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L920" class="LineNr"> 920 </span>  before-before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
-<span id="L921" class="LineNr"> 921 </span>  <span class="muControl">return-unless</span> before-before-cursor, <span class="Constant">0/false</span>  <span class="Comment"># cursor is at start of editor</span>
+<span id="L920" class="LineNr"> 920 </span>  before-before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
+<span id="L921" class="LineNr"> 921 </span>  <span class="muControl">return-unless</span> before-before-cursor,<span class="Constant"> false</span>  <span class="Comment"># cursor is at start of editor</span>
 <span id="L922" class="LineNr"> 922 </span>  char-before-cursor:char <span class="Special">&lt;-</span> get *before-cursor, <span class="Constant">value:offset</span>
 <span id="L923" class="LineNr"> 923 </span>  cursor-after-newline?:bool <span class="Special">&lt;-</span> equal char-before-cursor, <span class="Constant">10/newline</span>
-<span id="L924" class="LineNr"> 924 </span>  <span class="muControl">return-if</span> cursor-after-newline?, <span class="Constant">0/false</span>
+<span id="L924" class="LineNr"> 924 </span>  <span class="muControl">return-if</span> cursor-after-newline?,<span class="Constant"> false</span>
 <span id="L925" class="LineNr"> 925 </span>  <span class="Comment"># if cursor is at left margin and not at start, but previous character is not a newline,</span>
 <span id="L926" class="LineNr"> 926 </span>  <span class="Comment"># then we're at start of a wrapped line</span>
-<span id="L927" class="LineNr"> 927 </span> <span class="muControl"> return</span> <span class="Constant">1/true</span>
+<span id="L927" class="LineNr"> 927 </span> <span class="muControl"> return</span><span class="Constant"> true</span>
 <span id="L928" class="LineNr"> 928 </span>]
 <span id="L929" class="LineNr"> 929 </span>
 <span id="L930" class="LineNr"> 930 </span><span class="Comment"># takes a pointer 'curr' into the doubly-linked list and its sentinel, counts</span>
@@ -999,7 +999,7 @@ if ('onhashchange' in window) {
 <span id="L937" class="LineNr"> 937 </span>  at-start?:bool <span class="Special">&lt;-</span> equal curr, start
 <span id="L938" class="LineNr"> 938 </span>  <span class="muControl">return-if</span> at-start?
 <span id="L939" class="LineNr"> 939 </span>  <span class="Delimiter">{</span>
-<span id="L940" class="LineNr"> 940 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
+<span id="L940" class="LineNr"> 940 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
 <span id="L941" class="LineNr"> 941 </span>    <span class="muControl">break-unless</span> curr
 <span id="L942" class="LineNr"> 942 </span>    at-start?:bool <span class="Special">&lt;-</span> equal curr, start
 <span id="L943" class="LineNr"> 943 </span>    <span class="muControl">break-if</span> at-start?
@@ -1157,8 +1157,8 @@ if ('onhashchange' in window) {
 <span id="L1095" class="LineNr">1095 </span>  <span class="Delimiter">{</span>
 <span id="L1096" class="LineNr">1096 </span>    paste-start?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65507/paste-start</span>
 <span id="L1097" class="LineNr">1097 </span>    <span class="muControl">break-unless</span> paste-start?
-<span id="L1098" class="LineNr">1098 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">indent?:offset</span>, <span class="Constant">0/false</span>
-<span id="L1099" class="LineNr">1099 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L1098" class="LineNr">1098 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">indent?:offset</span>,<span class="Constant"> false</span>
+<span id="L1099" class="LineNr">1099 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L1100" class="LineNr">1100 </span>  <span class="Delimiter">}</span>
 <span id="L1101" class="LineNr">1101 </span>]
 <span id="L1102" class="LineNr">1102 </span>
@@ -1166,8 +1166,8 @@ if ('onhashchange' in window) {
 <span id="L1104" class="LineNr">1104 </span>  <span class="Delimiter">{</span>
 <span id="L1105" class="LineNr">1105 </span>    paste-end?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65506/paste-end</span>
 <span id="L1106" class="LineNr">1106 </span>    <span class="muControl">break-unless</span> paste-end?
-<span id="L1107" class="LineNr">1107 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">indent?:offset</span>, <span class="Constant">1/true</span>
-<span id="L1108" class="LineNr">1108 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L1107" class="LineNr">1107 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">indent?:offset</span>,<span class="Constant"> true</span>
+<span id="L1108" class="LineNr">1108 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L1109" class="LineNr">1109 </span>  <span class="Delimiter">}</span>
 <span id="L1110" class="LineNr">1110 </span>]
 <span id="L1111" class="LineNr">1111 </span>
diff --git a/html/edit/003-shortcuts.mu.html b/html/edit/003-shortcuts.mu.html
index 9d7cd6d1..e507b83d 100644
--- a/html/edit/003-shortcuts.mu.html
+++ b/html/edit/003-shortcuts.mu.html
@@ -15,16 +15,16 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.Delimiter { color: #800080; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
-.Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -173,31 +173,31 @@ if ('onhashchange' in window) {
 <span id="L112" class="LineNr"> 112 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L113" class="LineNr"> 113 </span>  data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
 <span id="L114" class="LineNr"> 114 </span>  <span class="Comment"># if at start of text (before-cursor at § sentinel), return</span>
-<span id="L115" class="LineNr"> 115 </span>  <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
-<span id="L116" class="LineNr"> 116 </span>  <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L32'>prev</a>, <span class="Constant">0/no-more-render</span>, <span class="Constant">0/nothing-deleted</span>
+<span id="L115" class="LineNr"> 115 </span>  <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
+<span id="L116" class="LineNr"> 116 </span>  <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L38'>prev</a>,<span class="Constant"> false/no-more-render, null/nothing-deleted</span>
 <span id="L117" class="LineNr"> 117 </span>  trace<span class="Constant"> 10</span>, <span class="Constant">[app]</span>, <span class="Constant">[delete-before-cursor]</span>
 <span id="L118" class="LineNr"> 118 </span>  original-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L119" class="LineNr"> 119 </span>  scroll?:bool <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L156'>move-cursor-coordinates-left</a> editor
 <span id="L120" class="LineNr"> 120 </span>  backspaced-cell:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy before-cursor
 <span id="L121" class="LineNr"> 121 </span>  data <span class="Special">&lt;-</span> remove before-cursor, data  <span class="Comment"># will also neatly trim next/prev pointers in backspaced-cell/before-cursor</span>
-<span id="L122" class="LineNr"> 122 </span>  before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L122" class="LineNr"> 122 </span>  before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L123" class="LineNr"> 123 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L124" class="LineNr"> 124 </span>  <span class="muControl">return-if</span> scroll?, <span class="Constant">1/go-render</span>
+<span id="L124" class="LineNr"> 124 </span>  <span class="muControl">return-if</span> scroll?,<span class="Constant"> true/go-render</span>
 <span id="L125" class="LineNr"> 125 </span>  <a href='../081print.mu.html#L768'>screen-width</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L768'>screen-width</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L126" class="LineNr"> 126 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L127" class="LineNr"> 127 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L128" class="LineNr"> 128 </span>  <span class="Comment"># did we just backspace over a newline?</span>
 <span id="L129" class="LineNr"> 129 </span>  same-row?:bool <span class="Special">&lt;-</span> equal cursor-row, original-row
-<span id="L130" class="LineNr"> 130 </span>  <span class="muControl">return-unless</span> same-row?, <span class="Constant">1/go-render</span>
+<span id="L130" class="LineNr"> 130 </span>  <span class="muControl">return-unless</span> same-row?,<span class="Constant"> true/go-render</span>
 <span id="L131" class="LineNr"> 131 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
 <span id="L132" class="LineNr"> 132 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
-<span id="L133" class="LineNr"> 133 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L133" class="LineNr"> 133 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L134" class="LineNr"> 134 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, cursor-row, cursor-column
 <span id="L135" class="LineNr"> 135 </span>  curr-column:num <span class="Special">&lt;-</span> copy cursor-column
 <span id="L136" class="LineNr"> 136 </span>  <span class="Delimiter">{</span>
 <span id="L137" class="LineNr"> 137 </span>    <span class="Comment"># hit right margin? give up and let caller render</span>
 <span id="L138" class="LineNr"> 138 </span>    at-right?:bool <span class="Special">&lt;-</span> greater-or-equal curr-column, right
-<span id="L139" class="LineNr"> 139 </span>    <span class="muControl">return-if</span> at-right?, <span class="Constant">1/go-render</span>
+<span id="L139" class="LineNr"> 139 </span>    <span class="muControl">return-if</span> at-right?,<span class="Constant"> true/go-render</span>
 <span id="L140" class="LineNr"> 140 </span>    <span class="muControl">break-unless</span> curr
 <span id="L141" class="LineNr"> 141 </span>    <span class="Comment"># newline? done.</span>
 <span id="L142" class="LineNr"> 142 </span>    currc:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
@@ -205,19 +205,19 @@ if ('onhashchange' in window) {
 <span id="L144" class="LineNr"> 144 </span>    <span class="muControl">break-if</span> at-newline?
 <span id="L145" class="LineNr"> 145 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> print <a href='../081print.mu.html#L16'>screen</a>, currc
 <span id="L146" class="LineNr"> 146 </span>    curr-column <span class="Special">&lt;-</span> add curr-column,<span class="Constant"> 1</span>
-<span id="L147" class="LineNr"> 147 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L147" class="LineNr"> 147 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L148" class="LineNr"> 148 </span>   <span class="muControl"> loop</span>
 <span id="L149" class="LineNr"> 149 </span>  <span class="Delimiter">}</span>
 <span id="L150" class="LineNr"> 150 </span>  <span class="Comment"># we're guaranteed not to be at the right margin</span>
 <span id="L151" class="LineNr"> 151 </span>  space:char <span class="Special">&lt;-</span> copy <span class="Constant">32/space</span>
 <span id="L152" class="LineNr"> 152 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> print <a href='../081print.mu.html#L16'>screen</a>, space
-<span id="L153" class="LineNr"> 153 </span>  go-render? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L153" class="LineNr"> 153 </span>  go-render? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L154" class="LineNr"> 154 </span>]
 <span id="L155" class="LineNr"> 155 </span>
 <span id="L156" class="LineNr"> 156 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L156'>move-cursor-coordinates-left</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor [
 <span id="L157" class="LineNr"> 157 </span>  <span class="Constant">local-scope</span>
 <span id="L158" class="LineNr"> 158 </span>  <span class="Constant">load-inputs</span>
-<span id="L159" class="LineNr"> 159 </span>  go-render?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L159" class="LineNr"> 159 </span>  go-render?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L160" class="LineNr"> 160 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L161" class="LineNr"> 161 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L162" class="LineNr"> 162 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
@@ -241,7 +241,7 @@ if ('onhashchange' in window) {
 <span id="L180" class="LineNr"> 180 </span>  <span class="Delimiter">{</span>
 <span id="L181" class="LineNr"> 181 </span>    <span class="muControl">break-unless</span> top-of-screen?
 <span id="L182" class="LineNr"> 182 </span><span class="Constant">    &lt;scroll-up&gt;</span>
-<span id="L183" class="LineNr"> 183 </span>    go-render? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L183" class="LineNr"> 183 </span>    go-render? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L184" class="LineNr"> 184 </span>  <span class="Delimiter">}</span>
 <span id="L185" class="LineNr"> 185 </span>  <span class="Delimiter">{</span>
 <span id="L186" class="LineNr"> 186 </span>    <span class="Comment"># case 1: if previous character was newline, figure out how long the previous line is</span>
@@ -285,7 +285,7 @@ if ('onhashchange' in window) {
 <span id="L224" class="LineNr"> 224 </span>  at-start?:bool <span class="Special">&lt;-</span> equal curr, start
 <span id="L225" class="LineNr"> 225 </span>  <span class="muControl">return-if</span> at-start?
 <span id="L226" class="LineNr"> 226 </span>  <span class="Delimiter">{</span>
-<span id="L227" class="LineNr"> 227 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
+<span id="L227" class="LineNr"> 227 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
 <span id="L228" class="LineNr"> 228 </span>    <span class="muControl">break-unless</span> curr
 <span id="L229" class="LineNr"> 229 </span>    at-start?:bool <span class="Special">&lt;-</span> equal curr, start
 <span id="L230" class="LineNr"> 230 </span>    <span class="muControl">break-if</span> at-start?
@@ -436,14 +436,14 @@ if ('onhashchange' in window) {
 <span id="L375" class="LineNr"> 375 </span>  <span class="Constant">load-inputs</span>
 <span id="L376" class="LineNr"> 376 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L377" class="LineNr"> 377 </span>  data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L378" class="LineNr"> 378 </span>  deleted-cell:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
-<span id="L379" class="LineNr"> 379 </span>  <span class="muControl">return-unless</span> deleted-cell, <span class="Constant">0/don't-render</span>
+<span id="L378" class="LineNr"> 378 </span>  deleted-cell:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
+<span id="L379" class="LineNr"> 379 </span>  <span class="muControl">return-unless</span> deleted-cell,<span class="Constant"> false/don't-render</span>
 <span id="L380" class="LineNr"> 380 </span>  currc:char <span class="Special">&lt;-</span> get *deleted-cell, <span class="Constant">value:offset</span>
 <span id="L381" class="LineNr"> 381 </span>  data <span class="Special">&lt;-</span> remove deleted-cell, data
 <span id="L382" class="LineNr"> 382 </span>  deleted-newline?:bool <span class="Special">&lt;-</span> equal currc, <span class="Constant">10/newline</span>
-<span id="L383" class="LineNr"> 383 </span>  <span class="muControl">return-if</span> deleted-newline?, <span class="Constant">1/go-render</span>
+<span id="L383" class="LineNr"> 383 </span>  <span class="muControl">return-if</span> deleted-newline?,<span class="Constant"> true/go-render</span>
 <span id="L384" class="LineNr"> 384 </span>  <span class="Comment"># wasn't a newline? render rest of line</span>
-<span id="L385" class="LineNr"> 385 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor  <span class="Comment"># refresh after remove above</span>
+<span id="L385" class="LineNr"> 385 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor  <span class="Comment"># refresh after remove above</span>
 <span id="L386" class="LineNr"> 386 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L387" class="LineNr"> 387 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L388" class="LineNr"> 388 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, cursor-row, cursor-column
@@ -452,20 +452,20 @@ if ('onhashchange' in window) {
 <span id="L391" class="LineNr"> 391 </span>  <span class="Delimiter">{</span>
 <span id="L392" class="LineNr"> 392 </span>    <span class="Comment"># hit right margin? give up and let caller render</span>
 <span id="L393" class="LineNr"> 393 </span>    at-right?:bool <span class="Special">&lt;-</span> greater-or-equal curr-column, <a href='../081print.mu.html#L768'>screen-width</a>
-<span id="L394" class="LineNr"> 394 </span>    <span class="muControl">return-if</span> at-right?, <span class="Constant">1/go-render</span>
+<span id="L394" class="LineNr"> 394 </span>    <span class="muControl">return-if</span> at-right?,<span class="Constant"> true/go-render</span>
 <span id="L395" class="LineNr"> 395 </span>    <span class="muControl">break-unless</span> curr
 <span id="L396" class="LineNr"> 396 </span>    currc:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
 <span id="L397" class="LineNr"> 397 </span>    at-newline?:bool <span class="Special">&lt;-</span> equal currc, <span class="Constant">10/newline</span>
 <span id="L398" class="LineNr"> 398 </span>    <span class="muControl">break-if</span> at-newline?
 <span id="L399" class="LineNr"> 399 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> print <a href='../081print.mu.html#L16'>screen</a>, currc
 <span id="L400" class="LineNr"> 400 </span>    curr-column <span class="Special">&lt;-</span> add curr-column,<span class="Constant"> 1</span>
-<span id="L401" class="LineNr"> 401 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L401" class="LineNr"> 401 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L402" class="LineNr"> 402 </span>   <span class="muControl"> loop</span>
 <span id="L403" class="LineNr"> 403 </span>  <span class="Delimiter">}</span>
 <span id="L404" class="LineNr"> 404 </span>  <span class="Comment"># we're guaranteed not to be at the right margin</span>
 <span id="L405" class="LineNr"> 405 </span>  space:char <span class="Special">&lt;-</span> copy <span class="Constant">32/space</span>
 <span id="L406" class="LineNr"> 406 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> print <a href='../081print.mu.html#L16'>screen</a>, space
-<span id="L407" class="LineNr"> 407 </span>  go-render? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L407" class="LineNr"> 407 </span>  go-render? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L408" class="LineNr"> 408 </span>]
 <span id="L409" class="LineNr"> 409 </span>
 <span id="L410" class="LineNr"> 410 </span><span class="Comment"># right arrow</span>
@@ -497,7 +497,7 @@ if ('onhashchange' in window) {
 <span id="L436" class="LineNr"> 436 </span>    move-to-next-character?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65514/right-arrow</span>
 <span id="L437" class="LineNr"> 437 </span>    <span class="muControl">break-unless</span> move-to-next-character?
 <span id="L438" class="LineNr"> 438 </span>    <span class="Comment"># if not at end of text</span>
-<span id="L439" class="LineNr"> 439 </span>    next-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L439" class="LineNr"> 439 </span>    next-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L440" class="LineNr"> 440 </span>    <span class="muControl">break-unless</span> next-cursor
 <span id="L441" class="LineNr"> 441 </span>    <span class="Comment"># scan to next character</span>
 <span id="L442" class="LineNr"> 442 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
@@ -529,11 +529,11 @@ if ('onhashchange' in window) {
 <span id="L468" class="LineNr"> 468 </span>    cursor-column <span class="Special">&lt;-</span> copy left
 <span id="L469" class="LineNr"> 469 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
 <span id="L470" class="LineNr"> 470 </span>    below-screen?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-row, <a href='../081print.mu.html#L782'>screen-height</a>  <span class="Comment"># must be equal</span>
-<span id="L471" class="LineNr"> 471 </span>    <span class="muControl">return-unless</span> below-screen?, <span class="Constant">0/don't-render</span>
+<span id="L471" class="LineNr"> 471 </span>    <span class="muControl">return-unless</span> below-screen?,<span class="Constant"> false/don't-render</span>
 <span id="L472" class="LineNr"> 472 </span><span class="Constant">    &lt;scroll-down&gt;</span>
 <span id="L473" class="LineNr"> 473 </span>    cursor-row <span class="Special">&lt;-</span> subtract cursor-row,<span class="Constant"> 1</span>  <span class="Comment"># bring back into screen range</span>
 <span id="L474" class="LineNr"> 474 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
-<span id="L475" class="LineNr"> 475 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L475" class="LineNr"> 475 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L476" class="LineNr"> 476 </span>  <span class="Delimiter">}</span>
 <span id="L477" class="LineNr"> 477 </span>  <span class="Comment"># if the line wraps, move cursor to start of next row</span>
 <span id="L478" class="LineNr"> 478 </span>  <span class="Delimiter">{</span>
@@ -542,8 +542,8 @@ if ('onhashchange' in window) {
 <span id="L481" class="LineNr"> 481 </span>    at-wrap?:bool <span class="Special">&lt;-</span> equal cursor-column, wrap-column
 <span id="L482" class="LineNr"> 482 </span>    <span class="muControl">break-unless</span> at-wrap?
 <span id="L483" class="LineNr"> 483 </span>    <span class="Comment"># and if next character isn't newline</span>
-<span id="L484" class="LineNr"> 484 </span>    <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
-<span id="L485" class="LineNr"> 485 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L484" class="LineNr"> 484 </span>    <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
+<span id="L485" class="LineNr"> 485 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L486" class="LineNr"> 486 </span>    next-character:char <span class="Special">&lt;-</span> get *next, <span class="Constant">value:offset</span>
 <span id="L487" class="LineNr"> 487 </span>    newline?:bool <span class="Special">&lt;-</span> equal next-character, <span class="Constant">10/newline</span>
 <span id="L488" class="LineNr"> 488 </span>    <span class="muControl">break-if</span> newline?
@@ -552,16 +552,16 @@ if ('onhashchange' in window) {
 <span id="L491" class="LineNr"> 491 </span>    cursor-column <span class="Special">&lt;-</span> copy left
 <span id="L492" class="LineNr"> 492 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
 <span id="L493" class="LineNr"> 493 </span>    below-screen?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-row, <a href='../081print.mu.html#L782'>screen-height</a>  <span class="Comment"># must be equal</span>
-<span id="L494" class="LineNr"> 494 </span>    <span class="muControl">return-unless</span> below-screen?, <span class="Constant">0/no-more-render</span>
+<span id="L494" class="LineNr"> 494 </span>    <span class="muControl">return-unless</span> below-screen?,<span class="Constant"> false/no-more-render</span>
 <span id="L495" class="LineNr"> 495 </span><span class="Constant">    &lt;scroll-down&gt;</span>
 <span id="L496" class="LineNr"> 496 </span>    cursor-row <span class="Special">&lt;-</span> subtract cursor-row,<span class="Constant"> 1</span>  <span class="Comment"># bring back into screen range</span>
 <span id="L497" class="LineNr"> 497 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
-<span id="L498" class="LineNr"> 498 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L498" class="LineNr"> 498 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L499" class="LineNr"> 499 </span>  <span class="Delimiter">}</span>
 <span id="L500" class="LineNr"> 500 </span>  <span class="Comment"># otherwise move cursor one character right</span>
 <span id="L501" class="LineNr"> 501 </span>  cursor-column <span class="Special">&lt;-</span> add cursor-column,<span class="Constant"> 1</span>
 <span id="L502" class="LineNr"> 502 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L503" class="LineNr"> 503 </span>  go-render? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L503" class="LineNr"> 503 </span>  go-render? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L504" class="LineNr"> 504 </span>]
 <span id="L505" class="LineNr"> 505 </span>
 <span id="L506" class="LineNr"> 506 </span><span class="muScenario">scenario</span> editor-moves-cursor-to-next-line-with-right-arrow [
@@ -782,11 +782,11 @@ if ('onhashchange' in window) {
 <span id="L721" class="LineNr"> 721 </span>    <span class="muControl">break-unless</span> move-to-previous-character?
 <span id="L722" class="LineNr"> 722 </span>    trace<span class="Constant"> 10</span>, <span class="Constant">[app]</span>, <span class="Constant">[left arrow]</span>
 <span id="L723" class="LineNr"> 723 </span>    <span class="Comment"># if not at start of text (before-cursor at § sentinel)</span>
-<span id="L724" class="LineNr"> 724 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
-<span id="L725" class="LineNr"> 725 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L32'>prev</a>, <span class="Constant">0/don't-render</span>
+<span id="L724" class="LineNr"> 724 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
+<span id="L725" class="LineNr"> 725 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L38'>prev</a>,<span class="Constant"> false/don't-render</span>
 <span id="L726" class="LineNr"> 726 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
 <span id="L727" class="LineNr"> 727 </span>    go-render? <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L156'>move-cursor-coordinates-left</a> editor
-<span id="L728" class="LineNr"> 728 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L728" class="LineNr"> 728 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L729" class="LineNr"> 729 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L730" class="LineNr"> 730 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">1/left-arrow</span>
 <span id="L731" class="LineNr"> 731 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
@@ -1061,7 +1061,7 @@ if ('onhashchange' in window) {
 <span id="L1000" class="LineNr">1000 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L1000'>move-to-previous-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor [
 <span id="L1001" class="LineNr">1001 </span>  <span class="Constant">local-scope</span>
 <span id="L1002" class="LineNr">1002 </span>  <span class="Constant">load-inputs</span>
-<span id="L1003" class="LineNr">1003 </span>  go-render?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L1003" class="LineNr">1003 </span>  go-render?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L1004" class="LineNr">1004 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L1005" class="LineNr">1005 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L1006" class="LineNr">1006 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
@@ -1099,7 +1099,7 @@ if ('onhashchange' in window) {
 <span id="L1038" class="LineNr">1038 </span>    <span class="Delimiter">{</span>
 <span id="L1039" class="LineNr">1039 </span>      done?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, target-column
 <span id="L1040" class="LineNr">1040 </span>      <span class="muControl">break-if</span> done?
-<span id="L1041" class="LineNr">1041 </span>      curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1041" class="LineNr">1041 </span>      curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1042" class="LineNr">1042 </span>      <span class="muControl">break-unless</span> curr
 <span id="L1043" class="LineNr">1043 </span>      currc:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
 <span id="L1044" class="LineNr">1044 </span>      at-newline?:bool <span class="Special">&lt;-</span> equal currc, <span class="Constant">10/newline</span>
@@ -1117,7 +1117,7 @@ if ('onhashchange' in window) {
 <span id="L1056" class="LineNr">1056 </span>    <span class="Comment"># if cursor already at top, scroll up</span>
 <span id="L1057" class="LineNr">1057 </span>    <span class="muControl">break-unless</span> already-at-top?
 <span id="L1058" class="LineNr">1058 </span><span class="Constant">    &lt;scroll-up&gt;</span>
-<span id="L1059" class="LineNr">1059 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L1059" class="LineNr">1059 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L1060" class="LineNr">1060 </span>  <span class="Delimiter">}</span>
 <span id="L1061" class="LineNr">1061 </span>]
 <span id="L1062" class="LineNr">1062 </span>
@@ -1141,9 +1141,9 @@ if ('onhashchange' in window) {
 <span id="L1080" class="LineNr">1080 </span>  <span class="Delimiter">{</span>
 <span id="L1081" class="LineNr">1081 </span>    <span class="muControl">break-if</span> len
 <span id="L1082" class="LineNr">1082 </span>    <span class="Comment"># empty line; just skip this newline</span>
-<span id="L1083" class="LineNr">1083 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
-<span id="L1084" class="LineNr">1084 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L32'>prev</a>, curr
-<span id="L1085" class="LineNr">1085 </span>   <span class="muControl"> return</span> <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L1083" class="LineNr">1083 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
+<span id="L1084" class="LineNr">1084 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L38'>prev</a>, curr
+<span id="L1085" class="LineNr">1085 </span>   <span class="muControl"> return</span> <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L1086" class="LineNr">1086 </span>  <span class="Delimiter">}</span>
 <span id="L1087" class="LineNr">1087 </span>  _, max:num <span class="Special">&lt;-</span> divide-with-remainder len, max-line-length
 <span id="L1088" class="LineNr">1088 </span>  <span class="Comment"># remainder 0 =&gt; scan one width-worth</span>
@@ -1157,9 +1157,9 @@ if ('onhashchange' in window) {
 <span id="L1096" class="LineNr">1096 </span>  <span class="Delimiter">{</span>
 <span id="L1097" class="LineNr">1097 </span>    done?:bool <span class="Special">&lt;-</span> greater-or-equal count, max
 <span id="L1098" class="LineNr">1098 </span>    <span class="muControl">break-if</span> done?
-<span id="L1099" class="LineNr">1099 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
-<span id="L1100" class="LineNr">1100 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L1101" class="LineNr">1101 </span>    curr <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L1099" class="LineNr">1099 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
+<span id="L1100" class="LineNr">1100 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L1101" class="LineNr">1101 </span>    curr <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L1102" class="LineNr">1102 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
 <span id="L1103" class="LineNr">1103 </span>   <span class="muControl"> loop</span>
 <span id="L1104" class="LineNr">1104 </span>  <span class="Delimiter">}</span>
@@ -1472,19 +1472,19 @@ if ('onhashchange' in window) {
 <span id="L1411" class="LineNr">1411 </span>    <span class="muControl">break-if</span> before-cursor
 <span id="L1412" class="LineNr">1412 </span>    <span class="Delimiter">{</span>
 <span id="L1413" class="LineNr">1413 </span>      <span class="muControl">break-if</span> at-bottom-of-screen?
-<span id="L1414" class="LineNr">1414 </span>     <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1414" class="LineNr">1414 </span>     <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1415" class="LineNr">1415 </span>    <span class="Delimiter">}</span>
 <span id="L1416" class="LineNr">1416 </span>    <span class="Delimiter">{</span>
 <span id="L1417" class="LineNr">1417 </span>      <span class="muControl">break-unless</span> at-bottom-of-screen?
 <span id="L1418" class="LineNr">1418 </span>     <span class="muControl"> jump</span> <span class="Constant">+try-to-scroll</span>
 <span id="L1419" class="LineNr">1419 </span>    <span class="Delimiter">}</span>
 <span id="L1420" class="LineNr">1420 </span>  <span class="Delimiter">}</span>
-<span id="L1421" class="LineNr">1421 </span>  <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1421" class="LineNr">1421 </span>  <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1422" class="LineNr">1422 </span>  <span class="Delimiter">{</span>
-<span id="L1423" class="LineNr">1423 </span>    <span class="muControl">break-if</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1423" class="LineNr">1423 </span>    <span class="muControl">break-if</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1424" class="LineNr">1424 </span>    <span class="Delimiter">{</span>
 <span id="L1425" class="LineNr">1425 </span>      <span class="muControl">break-if</span> at-bottom-of-screen?
-<span id="L1426" class="LineNr">1426 </span>     <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1426" class="LineNr">1426 </span>     <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1427" class="LineNr">1427 </span>    <span class="Delimiter">}</span>
 <span id="L1428" class="LineNr">1428 </span>    <span class="Delimiter">{</span>
 <span id="L1429" class="LineNr">1429 </span>      <span class="muControl">break-unless</span> at-bottom-of-screen?
@@ -1498,22 +1498,22 @@ if ('onhashchange' in window) {
 <span id="L1437" class="LineNr">1437 </span>    target-column:num <span class="Special">&lt;-</span> copy cursor-column
 <span id="L1438" class="LineNr">1438 </span>    <span class="Comment"># scan to start of next line</span>
 <span id="L1439" class="LineNr">1439 </span>    <span class="Delimiter">{</span>
-<span id="L1440" class="LineNr">1440 </span>      <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
-<span id="L1441" class="LineNr">1441 </span>      <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1440" class="LineNr">1440 </span>      <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
+<span id="L1441" class="LineNr">1441 </span>      <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1442" class="LineNr">1442 </span>      done?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, right
 <span id="L1443" class="LineNr">1443 </span>      <span class="muControl">break-if</span> done?
 <span id="L1444" class="LineNr">1444 </span>      cursor-column <span class="Special">&lt;-</span> add cursor-column,<span class="Constant"> 1</span>
-<span id="L1445" class="LineNr">1445 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1445" class="LineNr">1445 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1446" class="LineNr">1446 </span>      c:char <span class="Special">&lt;-</span> get *next, <span class="Constant">value:offset</span>
 <span id="L1447" class="LineNr">1447 </span>      at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
 <span id="L1448" class="LineNr">1448 </span>      <span class="muControl">break-if</span> at-newline?
 <span id="L1449" class="LineNr">1449 </span>     <span class="muControl"> loop</span>
 <span id="L1450" class="LineNr">1450 </span>    <span class="Delimiter">}</span>
 <span id="L1451" class="LineNr">1451 </span>    <span class="Delimiter">{</span>
-<span id="L1452" class="LineNr">1452 </span>      <span class="muControl">break-if</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1452" class="LineNr">1452 </span>      <span class="muControl">break-if</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1453" class="LineNr">1453 </span>      <span class="Delimiter">{</span>
 <span id="L1454" class="LineNr">1454 </span>        <span class="muControl">break-if</span> at-bottom-of-screen?
-<span id="L1455" class="LineNr">1455 </span>       <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1455" class="LineNr">1455 </span>       <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1456" class="LineNr">1456 </span>      <span class="Delimiter">}</span>
 <span id="L1457" class="LineNr">1457 </span>      <span class="Delimiter">{</span>
 <span id="L1458" class="LineNr">1458 </span>        <span class="muControl">break-unless</span> at-bottom-of-screen?
@@ -1523,25 +1523,25 @@ if ('onhashchange' in window) {
 <span id="L1462" class="LineNr">1462 </span>    cursor-row <span class="Special">&lt;-</span> add cursor-row,<span class="Constant"> 1</span>
 <span id="L1463" class="LineNr">1463 </span>    cursor-column <span class="Special">&lt;-</span> copy left
 <span id="L1464" class="LineNr">1464 </span>    <span class="Delimiter">{</span>
-<span id="L1465" class="LineNr">1465 </span>      <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
-<span id="L1466" class="LineNr">1466 </span>      <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1465" class="LineNr">1465 </span>      <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
+<span id="L1466" class="LineNr">1466 </span>      <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1467" class="LineNr">1467 </span>      c:char <span class="Special">&lt;-</span> get *next, <span class="Constant">value:offset</span>
 <span id="L1468" class="LineNr">1468 </span>      at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
 <span id="L1469" class="LineNr">1469 </span>      <span class="muControl">break-if</span> at-newline?
 <span id="L1470" class="LineNr">1470 </span>      done?:bool <span class="Special">&lt;-</span> greater-or-equal cursor-column, target-column
 <span id="L1471" class="LineNr">1471 </span>      <span class="muControl">break-if</span> done?
 <span id="L1472" class="LineNr">1472 </span>      cursor-column <span class="Special">&lt;-</span> add cursor-column,<span class="Constant"> 1</span>
-<span id="L1473" class="LineNr">1473 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1473" class="LineNr">1473 </span>      before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1474" class="LineNr">1474 </span>     <span class="muControl"> loop</span>
 <span id="L1475" class="LineNr">1475 </span>    <span class="Delimiter">}</span>
 <span id="L1476" class="LineNr">1476 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L1477" class="LineNr">1477 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
 <span id="L1478" class="LineNr">1478 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
-<span id="L1479" class="LineNr">1479 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1479" class="LineNr">1479 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1480" class="LineNr">1480 </span>  <span class="Delimiter">}</span>
 <span id="L1481" class="LineNr">1481 </span><span class="Constant">  +try-to-scroll</span>
 <span id="L1482" class="LineNr">1482 </span><span class="Constant">  &lt;scroll-down&gt;</span>
-<span id="L1483" class="LineNr">1483 </span>  go-render? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L1483" class="LineNr">1483 </span>  go-render? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L1484" class="LineNr">1484 </span>]
 <span id="L1485" class="LineNr">1485 </span>
 <span id="L1486" class="LineNr">1486 </span><span class="muScenario">scenario</span> editor-adjusts-column-at-next-line [
@@ -1650,7 +1650,7 @@ if ('onhashchange' in window) {
 <span id="L1589" class="LineNr">1589 </span>    <a href='003-shortcuts.mu.html#L1610'>move-to-start-of-screen-line</a> editor
 <span id="L1590" class="LineNr">1590 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
 <span id="L1591" class="LineNr">1591 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L1592" class="LineNr">1592 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1592" class="LineNr">1592 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1593" class="LineNr">1593 </span>  <span class="Delimiter">}</span>
 <span id="L1594" class="LineNr">1594 </span>]
 <span id="L1595" class="LineNr">1595 </span>
@@ -1662,7 +1662,7 @@ if ('onhashchange' in window) {
 <span id="L1601" class="LineNr">1601 </span>    <a href='003-shortcuts.mu.html#L1610'>move-to-start-of-screen-line</a> editor
 <span id="L1602" class="LineNr">1602 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
 <span id="L1603" class="LineNr">1603 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L1604" class="LineNr">1604 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1604" class="LineNr">1604 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1605" class="LineNr">1605 </span>  <span class="Delimiter">}</span>
 <span id="L1606" class="LineNr">1606 </span>]
 <span id="L1607" class="LineNr">1607 </span>
@@ -1681,7 +1681,7 @@ if ('onhashchange' in window) {
 <span id="L1620" class="LineNr">1620 </span>    done?:bool <span class="Special">&lt;-</span> equal col, left
 <span id="L1621" class="LineNr">1621 </span>    <span class="muControl">break-if</span> done?
 <span id="L1622" class="LineNr">1622 </span>    assert curr, <span class="Constant">[move-to-start-of-line tried to move before start of text]</span>
-<span id="L1623" class="LineNr">1623 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> curr
+<span id="L1623" class="LineNr">1623 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> curr
 <span id="L1624" class="LineNr">1624 </span>    col <span class="Special">&lt;-</span> subtract col,<span class="Constant"> 1</span>
 <span id="L1625" class="LineNr">1625 </span>   <span class="muControl"> loop</span>
 <span id="L1626" class="LineNr">1626 </span>  <span class="Delimiter">}</span>
@@ -1875,7 +1875,7 @@ if ('onhashchange' in window) {
 <span id="L1814" class="LineNr">1814 </span>    <a href='003-shortcuts.mu.html#L1833'>move-to-end-of-line</a> editor
 <span id="L1815" class="LineNr">1815 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
 <span id="L1816" class="LineNr">1816 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L1817" class="LineNr">1817 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1817" class="LineNr">1817 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1818" class="LineNr">1818 </span>  <span class="Delimiter">}</span>
 <span id="L1819" class="LineNr">1819 </span>]
 <span id="L1820" class="LineNr">1820 </span>
@@ -1887,7 +1887,7 @@ if ('onhashchange' in window) {
 <span id="L1826" class="LineNr">1826 </span>    <a href='003-shortcuts.mu.html#L1833'>move-to-end-of-line</a> editor
 <span id="L1827" class="LineNr">1827 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
 <span id="L1828" class="LineNr">1828 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L1829" class="LineNr">1829 </span>   <span class="muControl"> return</span> <span class="Constant">0/don't-render</span>
+<span id="L1829" class="LineNr">1829 </span>   <span class="muControl"> return</span><span class="Constant"> false/don't-render</span>
 <span id="L1830" class="LineNr">1830 </span>  <span class="Delimiter">}</span>
 <span id="L1831" class="LineNr">1831 </span>]
 <span id="L1832" class="LineNr">1832 </span>
@@ -1899,8 +1899,8 @@ if ('onhashchange' in window) {
 <span id="L1838" class="LineNr">1838 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
 <span id="L1839" class="LineNr">1839 </span>  <span class="Comment"># while not at end of line, move</span>
 <span id="L1840" class="LineNr">1840 </span>  <span class="Delimiter">{</span>
-<span id="L1841" class="LineNr">1841 </span>    <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
-<span id="L1842" class="LineNr">1842 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>  <span class="Comment"># end of text</span>
+<span id="L1841" class="LineNr">1841 </span>    <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
+<span id="L1842" class="LineNr">1842 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>  <span class="Comment"># end of text</span>
 <span id="L1843" class="LineNr">1843 </span>    nextc:char <span class="Special">&lt;-</span> get *next, <span class="Constant">value:offset</span>
 <span id="L1844" class="LineNr">1844 </span>    at-end-of-line?:bool <span class="Special">&lt;-</span> equal nextc, <span class="Constant">10/newline</span>
 <span id="L1845" class="LineNr">1845 </span>    <span class="muControl">break-if</span> at-end-of-line?
@@ -1908,7 +1908,7 @@ if ('onhashchange' in window) {
 <span id="L1847" class="LineNr">1847 </span>    at-right?:bool <span class="Special">&lt;-</span> equal cursor-column, right
 <span id="L1848" class="LineNr">1848 </span>    <span class="muControl">break-if</span> at-right?
 <span id="L1849" class="LineNr">1849 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L1850" class="LineNr">1850 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L1850" class="LineNr">1850 </span>    before-cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L31'>next</a>
 <span id="L1851" class="LineNr">1851 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
 <span id="L1852" class="LineNr">1852 </span>   <span class="muControl"> loop</span>
 <span id="L1853" class="LineNr">1853 </span>  <span class="Delimiter">}</span>
@@ -2086,8 +2086,8 @@ if ('onhashchange' in window) {
 <span id="L2025" class="LineNr">2025 </span>  <span class="Delimiter">{</span>
 <span id="L2026" class="LineNr">2026 </span>    <span class="Comment"># if we have a wrapped line, give up and render the whole screen</span>
 <span id="L2027" class="LineNr">2027 </span>    wrap?:bool <span class="Special">&lt;-</span> greater-or-equal i, right
-<span id="L2028" class="LineNr">2028 </span>    <span class="muControl">return-if</span> wrap?, <span class="Constant">1/go-render</span>
-<span id="L2029" class="LineNr">2029 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L2028" class="LineNr">2028 </span>    <span class="muControl">return-if</span> wrap?,<span class="Constant"> true/go-render</span>
+<span id="L2029" class="LineNr">2029 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L2030" class="LineNr">2030 </span>    <span class="muControl">break-unless</span> curr
 <span id="L2031" class="LineNr">2031 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
 <span id="L2032" class="LineNr">2032 </span>    b:bool <span class="Special">&lt;-</span> equal c,<span class="Constant"> 10</span>
@@ -2102,11 +2102,11 @@ if ('onhashchange' in window) {
 <span id="L2041" class="LineNr">2041 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
 <span id="L2042" class="LineNr">2042 </span>  end:num <span class="Special">&lt;-</span> subtract right, left
 <span id="L2043" class="LineNr">2043 </span>  wrap?:bool <span class="Special">&lt;-</span> greater-or-equal old-row-len, end
-<span id="L2044" class="LineNr">2044 </span>  <span class="muControl">return-if</span> wrap?, <span class="Constant">1/go-render</span>
+<span id="L2044" class="LineNr">2044 </span>  <span class="muControl">return-if</span> wrap?,<span class="Constant"> true/go-render</span>
 <span id="L2045" class="LineNr">2045 </span>  curr-line:text <span class="Special">&lt;-</span> <a href='../061text.mu.html#L338'>buffer-to-array</a> buf
 <span id="L2046" class="LineNr">2046 </span>  curr-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L2047" class="LineNr">2047 </span>  <a href='003-shortcuts.mu.html#L2107'>render-code</a> <a href='../081print.mu.html#L16'>screen</a>, curr-line, curr-column, right, curr-row
-<span id="L2048" class="LineNr">2048 </span> <span class="muControl"> return</span> <span class="Constant">0/dont-render</span>
+<span id="L2048" class="LineNr">2048 </span> <span class="muControl"> return</span><span class="Constant"> false/dont-render</span>
 <span id="L2049" class="LineNr">2049 </span>]
 <span id="L2050" class="LineNr">2050 </span>
 <span id="L2051" class="LineNr">2051 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L2051'>delete-to-start-of-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>result:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char, editor:&amp;:editor [
@@ -2115,10 +2115,10 @@ if ('onhashchange' in window) {
 <span id="L2054" class="LineNr">2054 </span>  <span class="Comment"># compute range to delete</span>
 <span id="L2055" class="LineNr">2055 </span>  init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
 <span id="L2056" class="LineNr">2056 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L2057" class="LineNr">2057 </span>  update-top-of-screen?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L2057" class="LineNr">2057 </span>  update-top-of-screen?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L2058" class="LineNr">2058 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L2059" class="LineNr">2059 </span>  start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy before-cursor
-<span id="L2060" class="LineNr">2060 </span>  end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L2060" class="LineNr">2060 </span>  end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L2061" class="LineNr">2061 </span>  <span class="Delimiter">{</span>
 <span id="L2062" class="LineNr">2062 </span>    at-start-of-text?:bool <span class="Special">&lt;-</span> equal start, init
 <span id="L2063" class="LineNr">2063 </span>    <span class="muControl">break-if</span> at-start-of-text?
@@ -2128,13 +2128,13 @@ if ('onhashchange' in window) {
 <span id="L2067" class="LineNr">2067 </span>    <span class="Comment"># if we went past top-of-screen, make a note to update it as well</span>
 <span id="L2068" class="LineNr">2068 </span>    at-top-of-screen?:bool <span class="Special">&lt;-</span> equal start, top-of-screen
 <span id="L2069" class="LineNr">2069 </span>    update-top-of-screen?:bool <span class="Special">&lt;-</span> or update-top-of-screen?, at-top-of-screen?
-<span id="L2070" class="LineNr">2070 </span>    start <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> start
+<span id="L2070" class="LineNr">2070 </span>    start <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> start
 <span id="L2071" class="LineNr">2071 </span>    assert start, <span class="Constant">[delete-to-start-of-line tried to move before start of text]</span>
 <span id="L2072" class="LineNr">2072 </span>   <span class="muControl"> loop</span>
 <span id="L2073" class="LineNr">2073 </span>  <span class="Delimiter">}</span>
 <span id="L2074" class="LineNr">2074 </span>  <span class="Comment"># snip it out</span>
-<span id="L2075" class="LineNr">2075 </span>  result:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> start
-<span id="L2076" class="LineNr">2076 </span>  <a href='../065duplex_list.mu.html#L385'>remove-between</a> start, end
+<span id="L2075" class="LineNr">2075 </span>  result:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> start
+<span id="L2076" class="LineNr">2076 </span>  <a href='../065duplex_list.mu.html#L391'>remove-between</a> start, end
 <span id="L2077" class="LineNr">2077 </span>  <span class="Comment"># update top-of-screen if it's just been invalidated</span>
 <span id="L2078" class="LineNr">2078 </span>  <span class="Delimiter">{</span>
 <span id="L2079" class="LineNr">2079 </span>    <span class="muControl">break-unless</span> update-top-of-screen?
@@ -2656,7 +2656,7 @@ if ('onhashchange' in window) {
 <span id="L2595" class="LineNr">2595 </span>  <span class="Constant">local-scope</span>
 <span id="L2596" class="LineNr">2596 </span>  <span class="Constant">load-inputs</span>
 <span id="L2597" class="LineNr">2597 </span>  <span class="Comment"># if we deleted nothing, there's nothing to render</span>
-<span id="L2598" class="LineNr">2598 </span>  <span class="muControl">return-unless</span> deleted-cells, <span class="Constant">0/dont-render</span>
+<span id="L2598" class="LineNr">2598 </span>  <span class="muControl">return-unless</span> deleted-cells,<span class="Constant"> false/dont-render</span>
 <span id="L2599" class="LineNr">2599 </span>  <span class="Comment"># if the line used to wrap before, give up and render the whole screen</span>
 <span id="L2600" class="LineNr">2600 </span>  curr-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L2601" class="LineNr">2601 </span>  num-deleted-cells:num <span class="Special">&lt;-</span> length deleted-cells
@@ -2665,9 +2665,9 @@ if ('onhashchange' in window) {
 <span id="L2604" class="LineNr">2604 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
 <span id="L2605" class="LineNr">2605 </span>  end:num <span class="Special">&lt;-</span> subtract right, left
 <span id="L2606" class="LineNr">2606 </span>  wrap?:bool <span class="Special">&lt;-</span> greater-or-equal old-row-len, end
-<span id="L2607" class="LineNr">2607 </span>  <span class="muControl">return-if</span> wrap?, <span class="Constant">1/go-render</span>
+<span id="L2607" class="LineNr">2607 </span>  <span class="muControl">return-if</span> wrap?,<span class="Constant"> true/go-render</span>
 <span id="L2608" class="LineNr">2608 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L2609" class="LineNr">2609 </span> <span class="muControl"> return</span> <span class="Constant">0/dont-render</span>
+<span id="L2609" class="LineNr">2609 </span> <span class="muControl"> return</span><span class="Constant"> false/dont-render</span>
 <span id="L2610" class="LineNr">2610 </span>]
 <span id="L2611" class="LineNr">2611 </span>
 <span id="L2612" class="LineNr">2612 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L2612'>delete-to-end-of-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>result:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char, editor:&amp;:editor [
@@ -2675,19 +2675,19 @@ if ('onhashchange' in window) {
 <span id="L2614" class="LineNr">2614 </span>  <span class="Constant">load-inputs</span>
 <span id="L2615" class="LineNr">2615 </span>  <span class="Comment"># compute range to delete</span>
 <span id="L2616" class="LineNr">2616 </span>  start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L2617" class="LineNr">2617 </span>  end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> start
+<span id="L2617" class="LineNr">2617 </span>  end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> start
 <span id="L2618" class="LineNr">2618 </span>  <span class="Delimiter">{</span>
-<span id="L2619" class="LineNr">2619 </span>    at-end-of-text?:bool <span class="Special">&lt;-</span> equal end, <span class="Constant">0/null</span>
+<span id="L2619" class="LineNr">2619 </span>    at-end-of-text?:bool <span class="Special">&lt;-</span> equal end,<span class="Constant"> null</span>
 <span id="L2620" class="LineNr">2620 </span>    <span class="muControl">break-if</span> at-end-of-text?
 <span id="L2621" class="LineNr">2621 </span>    curr:char <span class="Special">&lt;-</span> get *end, <span class="Constant">value:offset</span>
 <span id="L2622" class="LineNr">2622 </span>    at-end-of-line?:bool <span class="Special">&lt;-</span> equal curr, <span class="Constant">10/newline</span>
 <span id="L2623" class="LineNr">2623 </span>    <span class="muControl">break-if</span> at-end-of-line?
-<span id="L2624" class="LineNr">2624 </span>    end <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> end
+<span id="L2624" class="LineNr">2624 </span>    end <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> end
 <span id="L2625" class="LineNr">2625 </span>   <span class="muControl"> loop</span>
 <span id="L2626" class="LineNr">2626 </span>  <span class="Delimiter">}</span>
 <span id="L2627" class="LineNr">2627 </span>  <span class="Comment"># snip it out</span>
-<span id="L2628" class="LineNr">2628 </span>  result <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> start
-<span id="L2629" class="LineNr">2629 </span>  <a href='../065duplex_list.mu.html#L385'>remove-between</a> start, end
+<span id="L2628" class="LineNr">2628 </span>  result <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> start
+<span id="L2629" class="LineNr">2629 </span>  <a href='../065duplex_list.mu.html#L391'>remove-between</a> start, end
 <span id="L2630" class="LineNr">2630 </span>]
 <span id="L2631" class="LineNr">2631 </span>
 <span id="L2632" class="LineNr">2632 </span><span class="muScenario">scenario</span> editor-deletes-to-end-of-line-with-ctrl-k-2 [
@@ -2897,1617 +2897,1630 @@ if ('onhashchange' in window) {
 <span id="L2836" class="LineNr">2836 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
 <span id="L2837" class="LineNr">2837 </span>  max:num <span class="Special">&lt;-</span> subtract right, left
 <span id="L2838" class="LineNr">2838 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy top-of-screen
-<span id="L2839" class="LineNr">2839 </span>  top-of-screen <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L2849'>before-start-of-next-line</a> top-of-screen, max
+<span id="L2839" class="LineNr">2839 </span>  top-of-screen <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L2862'>before-start-of-next-line</a> top-of-screen, max
 <span id="L2840" class="LineNr">2840 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
 <span id="L2841" class="LineNr">2841 </span>  no-movement?:bool <span class="Special">&lt;-</span> equal old-top, top-of-screen
-<span id="L2842" class="LineNr">2842 </span>  <span class="muControl">return-if</span> no-movement?, <span class="Constant">0/don't-render</span>
+<span id="L2842" class="LineNr">2842 </span>  <span class="muControl">return-if</span> no-movement?,<span class="Constant"> false/don't-render</span>
 <span id="L2843" class="LineNr">2843 </span>]
 <span id="L2844" class="LineNr">2844 </span>
-<span id="L2845" class="LineNr">2845 </span><span class="Comment"># Takes a pointer into the doubly-linked list, scans ahead at most 'max'</span>
-<span id="L2846" class="LineNr">2846 </span><span class="Comment"># positions until the next newline.</span>
-<span id="L2847" class="LineNr">2847 </span><span class="Comment"># Returns original if no next newline.</span>
-<span id="L2848" class="LineNr">2848 </span><span class="Comment"># Beware: never return null pointer.</span>
-<span id="L2849" class="LineNr">2849 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L2849'>before-start-of-next-line</a> original:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char, max:num<span class="muRecipe"> -&gt; </span>curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char [
-<span id="L2850" class="LineNr">2850 </span>  <span class="Constant">local-scope</span>
-<span id="L2851" class="LineNr">2851 </span>  <span class="Constant">load-inputs</span>
-<span id="L2852" class="LineNr">2852 </span>  count:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
-<span id="L2853" class="LineNr">2853 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy original
-<span id="L2854" class="LineNr">2854 </span>  <span class="Comment"># skip the initial newline if it exists</span>
-<span id="L2855" class="LineNr">2855 </span>  <span class="Delimiter">{</span>
-<span id="L2856" class="LineNr">2856 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
-<span id="L2857" class="LineNr">2857 </span>    at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
-<span id="L2858" class="LineNr">2858 </span>    <span class="muControl">break-unless</span> at-newline?
-<span id="L2859" class="LineNr">2859 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L2860" class="LineNr">2860 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
-<span id="L2861" class="LineNr">2861 </span>  <span class="Delimiter">}</span>
-<span id="L2862" class="LineNr">2862 </span>  <span class="Delimiter">{</span>
-<span id="L2863" class="LineNr">2863 </span>    <span class="muControl">return-unless</span> curr, original
-<span id="L2864" class="LineNr">2864 </span>    done?:bool <span class="Special">&lt;-</span> greater-or-equal count, max
-<span id="L2865" class="LineNr">2865 </span>    <span class="muControl">break-if</span> done?
-<span id="L2866" class="LineNr">2866 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
-<span id="L2867" class="LineNr">2867 </span>    at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
-<span id="L2868" class="LineNr">2868 </span>    <span class="muControl">break-if</span> at-newline?
-<span id="L2869" class="LineNr">2869 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L2870" class="LineNr">2870 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
-<span id="L2871" class="LineNr">2871 </span>   <span class="muControl"> loop</span>
-<span id="L2872" class="LineNr">2872 </span>  <span class="Delimiter">}</span>
-<span id="L2873" class="LineNr">2873 </span>  <span class="muControl">return-unless</span> curr, original
-<span id="L2874" class="LineNr">2874 </span> <span class="muControl"> return</span> curr
-<span id="L2875" class="LineNr">2875 </span>]
-<span id="L2876" class="LineNr">2876 </span>
-<span id="L2877" class="LineNr">2877 </span><span class="muScenario">scenario</span> editor-scrolls-down-past-wrapped-line-using-arrow-keys [
-<span id="L2878" class="LineNr">2878 </span>  <span class="Constant">local-scope</span>
-<span id="L2879" class="LineNr">2879 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L2880" class="LineNr">2880 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L2881" class="LineNr">2881 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
-<span id="L2882" class="LineNr">2882 </span>  <span class="Comment"># other lines</span>
-<span id="L2883" class="LineNr">2883 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
-<span id="L2884" class="LineNr">2884 </span><span class="Constant">g</span>
-<span id="L2885" class="LineNr">2885 </span><span class="Constant">h</span>
-<span id="L2886" class="LineNr">2886 </span><span class="Constant">i]</span>
-<span id="L2887" class="LineNr">2887 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L2888" class="LineNr">2888 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L2889" class="LineNr">2889 </span>  screen-should-contain [
-<span id="L2890" class="LineNr">2890 </span>   <span class="Constant"> .          .</span>
-<span id="L2891" class="LineNr">2891 </span>   <span class="Constant"> .abcd↩     .</span>
-<span id="L2892" class="LineNr">2892 </span>   <span class="Constant"> .ef        .</span>
-<span id="L2893" class="LineNr">2893 </span>   <span class="Constant"> .g         .</span>
-<span id="L2894" class="LineNr">2894 </span>  ]
-<span id="L2895" class="LineNr">2895 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
-<span id="L2896" class="LineNr">2896 </span>  assume-console [
-<span id="L2897" class="LineNr">2897 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-<span id="L2898" class="LineNr">2898 </span>    press down-arrow
-<span id="L2899" class="LineNr">2899 </span>  ]
-<span id="L2900" class="LineNr">2900 </span>  run [
-<span id="L2901" class="LineNr">2901 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L2902" class="LineNr">2902 </span>  ]
-<span id="L2903" class="LineNr">2903 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L2904" class="LineNr">2904 </span>  screen-should-contain [
-<span id="L2905" class="LineNr">2905 </span>   <span class="Constant"> .          .</span>
-<span id="L2906" class="LineNr">2906 </span>   <span class="Constant"> .ef        .</span>
-<span id="L2907" class="LineNr">2907 </span>   <span class="Constant"> .g         .</span>
-<span id="L2908" class="LineNr">2908 </span>   <span class="Constant"> .h         .</span>
-<span id="L2909" class="LineNr">2909 </span>  ]
-<span id="L2910" class="LineNr">2910 </span>]
-<span id="L2911" class="LineNr">2911 </span>
-<span id="L2912" class="LineNr">2912 </span><span class="muScenario">scenario</span> editor-scrolls-down-past-wrapped-line-using-arrow-keys-2 [
-<span id="L2913" class="LineNr">2913 </span>  <span class="Constant">local-scope</span>
-<span id="L2914" class="LineNr">2914 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L2915" class="LineNr">2915 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L2916" class="LineNr">2916 </span>  <span class="Comment"># editor starts with a long line wrapping twice</span>
-<span id="L2917" class="LineNr">2917 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdefghij</span>
-<span id="L2918" class="LineNr">2918 </span><span class="Constant">k</span>
-<span id="L2919" class="LineNr">2919 </span><span class="Constant">l</span>
-<span id="L2920" class="LineNr">2920 </span><span class="Constant">m]</span>
-<span id="L2921" class="LineNr">2921 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L2922" class="LineNr">2922 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
-<span id="L2923" class="LineNr">2923 </span>  assume-console [
-<span id="L2924" class="LineNr">2924 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-<span id="L2925" class="LineNr">2925 </span>    press down-arrow
-<span id="L2926" class="LineNr">2926 </span>  ]
-<span id="L2927" class="LineNr">2927 </span>  run [
-<span id="L2928" class="LineNr">2928 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L2929" class="LineNr">2929 </span>  ]
-<span id="L2930" class="LineNr">2930 </span>  <span class="Comment"># screen shows partial wrapped line containing a wrap icon</span>
-<span id="L2931" class="LineNr">2931 </span>  screen-should-contain [
-<span id="L2932" class="LineNr">2932 </span>   <span class="Constant"> .          .</span>
-<span id="L2933" class="LineNr">2933 </span>   <span class="Constant"> .efgh↩     .</span>
-<span id="L2934" class="LineNr">2934 </span>   <span class="Constant"> .ij        .</span>
-<span id="L2935" class="LineNr">2935 </span>   <span class="Constant"> .k         .</span>
-<span id="L2936" class="LineNr">2936 </span>  ]
-<span id="L2937" class="LineNr">2937 </span>  <span class="Comment"># scroll down again</span>
-<span id="L2938" class="LineNr">2938 </span>  assume-console [
-<span id="L2939" class="LineNr">2939 </span>    press down-arrow
-<span id="L2940" class="LineNr">2940 </span>  ]
-<span id="L2941" class="LineNr">2941 </span>  run [
-<span id="L2942" class="LineNr">2942 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L2943" class="LineNr">2943 </span>  ]
-<span id="L2944" class="LineNr">2944 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L2945" class="LineNr">2945 </span>  screen-should-contain [
-<span id="L2946" class="LineNr">2946 </span>   <span class="Constant"> .          .</span>
+<span id="L2845" class="LineNr">2845 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L888'>&lt;scroll-down2&gt;</a></span> [
+<span id="L2846" class="LineNr">2846 </span>  trace<span class="Constant"> 10</span>, <span class="Constant">[app]</span>, <span class="Constant">[scroll down]</span>
+<span id="L2847" class="LineNr">2847 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L2848" class="LineNr">2848 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
+<span id="L2849" class="LineNr">2849 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
+<span id="L2850" class="LineNr">2850 </span>  max:num <span class="Special">&lt;-</span> subtract right, left
+<span id="L2851" class="LineNr">2851 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy top-of-screen
+<span id="L2852" class="LineNr">2852 </span>  top-of-screen <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L2862'>before-start-of-next-line</a> top-of-screen, max
+<span id="L2853" class="LineNr">2853 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
+<span id="L2854" class="LineNr">2854 </span>  no-movement?:bool <span class="Special">&lt;-</span> equal old-top, top-of-screen
+<span id="L2855" class="LineNr">2855 </span>  <span class="muControl">return-if</span> no-movement?
+<span id="L2856" class="LineNr">2856 </span>]
+<span id="L2857" class="LineNr">2857 </span>
+<span id="L2858" class="LineNr">2858 </span><span class="Comment"># Takes a pointer into the doubly-linked list, scans ahead at most 'max'</span>
+<span id="L2859" class="LineNr">2859 </span><span class="Comment"># positions until the next newline.</span>
+<span id="L2860" class="LineNr">2860 </span><span class="Comment"># Returns original if no next newline.</span>
+<span id="L2861" class="LineNr">2861 </span><span class="Comment"># Beware: never return null pointer.</span>
+<span id="L2862" class="LineNr">2862 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L2862'>before-start-of-next-line</a> original:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char, max:num<span class="muRecipe"> -&gt; </span>curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char [
+<span id="L2863" class="LineNr">2863 </span>  <span class="Constant">local-scope</span>
+<span id="L2864" class="LineNr">2864 </span>  <span class="Constant">load-inputs</span>
+<span id="L2865" class="LineNr">2865 </span>  count:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
+<span id="L2866" class="LineNr">2866 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy original
+<span id="L2867" class="LineNr">2867 </span>  <span class="Comment"># skip the initial newline if it exists</span>
+<span id="L2868" class="LineNr">2868 </span>  <span class="Delimiter">{</span>
+<span id="L2869" class="LineNr">2869 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
+<span id="L2870" class="LineNr">2870 </span>    at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
+<span id="L2871" class="LineNr">2871 </span>    <span class="muControl">break-unless</span> at-newline?
+<span id="L2872" class="LineNr">2872 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L2873" class="LineNr">2873 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
+<span id="L2874" class="LineNr">2874 </span>  <span class="Delimiter">}</span>
+<span id="L2875" class="LineNr">2875 </span>  <span class="Delimiter">{</span>
+<span id="L2876" class="LineNr">2876 </span>    <span class="muControl">return-unless</span> curr, original
+<span id="L2877" class="LineNr">2877 </span>    done?:bool <span class="Special">&lt;-</span> greater-or-equal count, max
+<span id="L2878" class="LineNr">2878 </span>    <span class="muControl">break-if</span> done?
+<span id="L2879" class="LineNr">2879 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
+<span id="L2880" class="LineNr">2880 </span>    at-newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
+<span id="L2881" class="LineNr">2881 </span>    <span class="muControl">break-if</span> at-newline?
+<span id="L2882" class="LineNr">2882 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L2883" class="LineNr">2883 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
+<span id="L2884" class="LineNr">2884 </span>   <span class="muControl"> loop</span>
+<span id="L2885" class="LineNr">2885 </span>  <span class="Delimiter">}</span>
+<span id="L2886" class="LineNr">2886 </span>  <span class="muControl">return-unless</span> curr, original
+<span id="L2887" class="LineNr">2887 </span> <span class="muControl"> return</span> curr
+<span id="L2888" class="LineNr">2888 </span>]
+<span id="L2889" class="LineNr">2889 </span>
+<span id="L2890" class="LineNr">2890 </span><span class="muScenario">scenario</span> editor-scrolls-down-past-wrapped-line-using-arrow-keys [
+<span id="L2891" class="LineNr">2891 </span>  <span class="Constant">local-scope</span>
+<span id="L2892" class="LineNr">2892 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L2893" class="LineNr">2893 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L2894" class="LineNr">2894 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
+<span id="L2895" class="LineNr">2895 </span>  <span class="Comment"># other lines</span>
+<span id="L2896" class="LineNr">2896 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
+<span id="L2897" class="LineNr">2897 </span><span class="Constant">g</span>
+<span id="L2898" class="LineNr">2898 </span><span class="Constant">h</span>
+<span id="L2899" class="LineNr">2899 </span><span class="Constant">i]</span>
+<span id="L2900" class="LineNr">2900 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L2901" class="LineNr">2901 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L2902" class="LineNr">2902 </span>  screen-should-contain [
+<span id="L2903" class="LineNr">2903 </span>   <span class="Constant"> .          .</span>
+<span id="L2904" class="LineNr">2904 </span>   <span class="Constant"> .abcd↩     .</span>
+<span id="L2905" class="LineNr">2905 </span>   <span class="Constant"> .ef        .</span>
+<span id="L2906" class="LineNr">2906 </span>   <span class="Constant"> .g         .</span>
+<span id="L2907" class="LineNr">2907 </span>  ]
+<span id="L2908" class="LineNr">2908 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
+<span id="L2909" class="LineNr">2909 </span>  assume-console [
+<span id="L2910" class="LineNr">2910 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<span id="L2911" class="LineNr">2911 </span>    press down-arrow
+<span id="L2912" class="LineNr">2912 </span>  ]
+<span id="L2913" class="LineNr">2913 </span>  run [
+<span id="L2914" class="LineNr">2914 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L2915" class="LineNr">2915 </span>  ]
+<span id="L2916" class="LineNr">2916 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L2917" class="LineNr">2917 </span>  screen-should-contain [
+<span id="L2918" class="LineNr">2918 </span>   <span class="Constant"> .          .</span>
+<span id="L2919" class="LineNr">2919 </span>   <span class="Constant"> .ef        .</span>
+<span id="L2920" class="LineNr">2920 </span>   <span class="Constant"> .g         .</span>
+<span id="L2921" class="LineNr">2921 </span>   <span class="Constant"> .h         .</span>
+<span id="L2922" class="LineNr">2922 </span>  ]
+<span id="L2923" class="LineNr">2923 </span>]
+<span id="L2924" class="LineNr">2924 </span>
+<span id="L2925" class="LineNr">2925 </span><span class="muScenario">scenario</span> editor-scrolls-down-past-wrapped-line-using-arrow-keys-2 [
+<span id="L2926" class="LineNr">2926 </span>  <span class="Constant">local-scope</span>
+<span id="L2927" class="LineNr">2927 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L2928" class="LineNr">2928 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L2929" class="LineNr">2929 </span>  <span class="Comment"># editor starts with a long line wrapping twice</span>
+<span id="L2930" class="LineNr">2930 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdefghij</span>
+<span id="L2931" class="LineNr">2931 </span><span class="Constant">k</span>
+<span id="L2932" class="LineNr">2932 </span><span class="Constant">l</span>
+<span id="L2933" class="LineNr">2933 </span><span class="Constant">m]</span>
+<span id="L2934" class="LineNr">2934 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L2935" class="LineNr">2935 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
+<span id="L2936" class="LineNr">2936 </span>  assume-console [
+<span id="L2937" class="LineNr">2937 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<span id="L2938" class="LineNr">2938 </span>    press down-arrow
+<span id="L2939" class="LineNr">2939 </span>  ]
+<span id="L2940" class="LineNr">2940 </span>  run [
+<span id="L2941" class="LineNr">2941 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L2942" class="LineNr">2942 </span>  ]
+<span id="L2943" class="LineNr">2943 </span>  <span class="Comment"># screen shows partial wrapped line containing a wrap icon</span>
+<span id="L2944" class="LineNr">2944 </span>  screen-should-contain [
+<span id="L2945" class="LineNr">2945 </span>   <span class="Constant"> .          .</span>
+<span id="L2946" class="LineNr">2946 </span>   <span class="Constant"> .efgh↩     .</span>
 <span id="L2947" class="LineNr">2947 </span>   <span class="Constant"> .ij        .</span>
 <span id="L2948" class="LineNr">2948 </span>   <span class="Constant"> .k         .</span>
-<span id="L2949" class="LineNr">2949 </span>   <span class="Constant"> .l         .</span>
-<span id="L2950" class="LineNr">2950 </span>  ]
-<span id="L2951" class="LineNr">2951 </span>]
-<span id="L2952" class="LineNr">2952 </span>
-<span id="L2953" class="LineNr">2953 </span><span class="muScenario">scenario</span> editor-scrolls-down-when-line-wraps [
-<span id="L2954" class="LineNr">2954 </span>  <span class="Constant">local-scope</span>
-<span id="L2955" class="LineNr">2955 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L2956" class="LineNr">2956 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
-<span id="L2957" class="LineNr">2957 </span>  <span class="Comment"># editor contains a long line in the third line</span>
-<span id="L2958" class="LineNr">2958 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L2959" class="LineNr">2959 </span><span class="Constant">b</span>
-<span id="L2960" class="LineNr">2960 </span><span class="Constant">cdef]</span>
-<span id="L2961" class="LineNr">2961 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L2962" class="LineNr">2962 </span>  <span class="Comment"># position cursor at end, type a character</span>
-<span id="L2963" class="LineNr">2963 </span>  assume-console [
-<span id="L2964" class="LineNr">2964 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 4</span>
-<span id="L2965" class="LineNr">2965 </span>    type <span class="Constant">[g]</span>
-<span id="L2966" class="LineNr">2966 </span>  ]
-<span id="L2967" class="LineNr">2967 </span>  run [
-<span id="L2968" class="LineNr">2968 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L2969" class="LineNr">2969 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L2970" class="LineNr">2970 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
-<span id="L2971" class="LineNr">2971 </span>  ]
-<span id="L2972" class="LineNr">2972 </span>  <span class="Comment"># screen scrolls</span>
-<span id="L2973" class="LineNr">2973 </span>  screen-should-contain [
-<span id="L2974" class="LineNr">2974 </span>   <span class="Constant"> .     .</span>
-<span id="L2975" class="LineNr">2975 </span>   <span class="Constant"> .b    .</span>
-<span id="L2976" class="LineNr">2976 </span><span class="Constant">    .cdef↩.</span>
-<span id="L2977" class="LineNr">2977 </span>   <span class="Constant"> .g    .</span>
-<span id="L2978" class="LineNr">2978 </span>  ]
-<span id="L2979" class="LineNr">2979 </span>  memory-should-contain [
-<span id="L2980" class="LineNr">2980 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-<span id="L2981" class="LineNr">2981 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
-<span id="L2982" class="LineNr">2982 </span>  ]
-<span id="L2983" class="LineNr">2983 </span>]
-<span id="L2984" class="LineNr">2984 </span>
-<span id="L2985" class="LineNr">2985 </span><span class="muScenario">scenario</span> editor-stops-scrolling-once-bottom-is-visible [
-<span id="L2986" class="LineNr">2986 </span>  <span class="Constant">local-scope</span>
-<span id="L2987" class="LineNr">2987 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L2988" class="LineNr">2988 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L2989" class="LineNr">2989 </span>  <span class="Comment"># initialize editor with 2 lines</span>
-<span id="L2990" class="LineNr">2990 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L2991" class="LineNr">2991 </span><span class="Constant">b]</span>
-<span id="L2992" class="LineNr">2992 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L2993" class="LineNr">2993 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L2994" class="LineNr">2994 </span>  screen-should-contain [
-<span id="L2995" class="LineNr">2995 </span>   <span class="Constant"> .          .</span>
-<span id="L2996" class="LineNr">2996 </span>   <span class="Constant"> .a         .</span>
-<span id="L2997" class="LineNr">2997 </span>   <span class="Constant"> .b         .</span>
-<span id="L2998" class="LineNr">2998 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L2999" class="LineNr">2999 </span>  ]
-<span id="L3000" class="LineNr">3000 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
-<span id="L3001" class="LineNr">3001 </span>  assume-console [
-<span id="L3002" class="LineNr">3002 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
-<span id="L3003" class="LineNr">3003 </span>    press down-arrow
-<span id="L3004" class="LineNr">3004 </span>  ]
-<span id="L3005" class="LineNr">3005 </span>  run [
-<span id="L3006" class="LineNr">3006 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3007" class="LineNr">3007 </span>  ]
-<span id="L3008" class="LineNr">3008 </span>  <span class="Comment"># no change since the bottom border was already visible</span>
-<span id="L3009" class="LineNr">3009 </span>  screen-should-contain [
-<span id="L3010" class="LineNr">3010 </span>   <span class="Constant"> .          .</span>
-<span id="L3011" class="LineNr">3011 </span>   <span class="Constant"> .a         .</span>
-<span id="L3012" class="LineNr">3012 </span>   <span class="Constant"> .b         .</span>
-<span id="L3013" class="LineNr">3013 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L3014" class="LineNr">3014 </span>  ]
-<span id="L3015" class="LineNr">3015 </span>]
-<span id="L3016" class="LineNr">3016 </span>
-<span id="L3017" class="LineNr">3017 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-newline [
-<span id="L3018" class="LineNr">3018 </span>  <span class="Constant">local-scope</span>
-<span id="L3019" class="LineNr">3019 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
-<span id="L3020" class="LineNr">3020 </span>  <span class="Comment"># position cursor after last line and type newline</span>
-<span id="L3021" class="LineNr">3021 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3022" class="LineNr">3022 </span><span class="Constant">b</span>
-<span id="L3023" class="LineNr">3023 </span><span class="Constant">c]</span>
-<span id="L3024" class="LineNr">3024 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3025" class="LineNr">3025 </span>  assume-console [
-<span id="L3026" class="LineNr">3026 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 4</span>
-<span id="L3027" class="LineNr">3027 </span>    type [
+<span id="L2949" class="LineNr">2949 </span>  ]
+<span id="L2950" class="LineNr">2950 </span>  <span class="Comment"># scroll down again</span>
+<span id="L2951" class="LineNr">2951 </span>  assume-console [
+<span id="L2952" class="LineNr">2952 </span>    press down-arrow
+<span id="L2953" class="LineNr">2953 </span>  ]
+<span id="L2954" class="LineNr">2954 </span>  run [
+<span id="L2955" class="LineNr">2955 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L2956" class="LineNr">2956 </span>  ]
+<span id="L2957" class="LineNr">2957 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L2958" class="LineNr">2958 </span>  screen-should-contain [
+<span id="L2959" class="LineNr">2959 </span>   <span class="Constant"> .          .</span>
+<span id="L2960" class="LineNr">2960 </span>   <span class="Constant"> .ij        .</span>
+<span id="L2961" class="LineNr">2961 </span>   <span class="Constant"> .k         .</span>
+<span id="L2962" class="LineNr">2962 </span>   <span class="Constant"> .l         .</span>
+<span id="L2963" class="LineNr">2963 </span>  ]
+<span id="L2964" class="LineNr">2964 </span>]
+<span id="L2965" class="LineNr">2965 </span>
+<span id="L2966" class="LineNr">2966 </span><span class="muScenario">scenario</span> editor-scrolls-down-when-line-wraps [
+<span id="L2967" class="LineNr">2967 </span>  <span class="Constant">local-scope</span>
+<span id="L2968" class="LineNr">2968 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L2969" class="LineNr">2969 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
+<span id="L2970" class="LineNr">2970 </span>  <span class="Comment"># editor contains a long line in the third line</span>
+<span id="L2971" class="LineNr">2971 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L2972" class="LineNr">2972 </span><span class="Constant">b</span>
+<span id="L2973" class="LineNr">2973 </span><span class="Constant">cdef]</span>
+<span id="L2974" class="LineNr">2974 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L2975" class="LineNr">2975 </span>  <span class="Comment"># position cursor at end, type a character</span>
+<span id="L2976" class="LineNr">2976 </span>  assume-console [
+<span id="L2977" class="LineNr">2977 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 4</span>
+<span id="L2978" class="LineNr">2978 </span>    type <span class="Constant">[g]</span>
+<span id="L2979" class="LineNr">2979 </span>  ]
+<span id="L2980" class="LineNr">2980 </span>  run [
+<span id="L2981" class="LineNr">2981 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L2982" class="LineNr">2982 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L2983" class="LineNr">2983 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L2984" class="LineNr">2984 </span>  ]
+<span id="L2985" class="LineNr">2985 </span>  <span class="Comment"># screen scrolls</span>
+<span id="L2986" class="LineNr">2986 </span>  screen-should-contain [
+<span id="L2987" class="LineNr">2987 </span>   <span class="Constant"> .     .</span>
+<span id="L2988" class="LineNr">2988 </span>   <span class="Constant"> .b    .</span>
+<span id="L2989" class="LineNr">2989 </span><span class="Constant">    .cdef↩.</span>
+<span id="L2990" class="LineNr">2990 </span>   <span class="Constant"> .g    .</span>
+<span id="L2991" class="LineNr">2991 </span>  ]
+<span id="L2992" class="LineNr">2992 </span>  memory-should-contain [
+<span id="L2993" class="LineNr">2993 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<span id="L2994" class="LineNr">2994 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
+<span id="L2995" class="LineNr">2995 </span>  ]
+<span id="L2996" class="LineNr">2996 </span>]
+<span id="L2997" class="LineNr">2997 </span>
+<span id="L2998" class="LineNr">2998 </span><span class="muScenario">scenario</span> editor-stops-scrolling-once-bottom-is-visible [
+<span id="L2999" class="LineNr">2999 </span>  <span class="Constant">local-scope</span>
+<span id="L3000" class="LineNr">3000 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3001" class="LineNr">3001 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3002" class="LineNr">3002 </span>  <span class="Comment"># initialize editor with 2 lines</span>
+<span id="L3003" class="LineNr">3003 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3004" class="LineNr">3004 </span><span class="Constant">b]</span>
+<span id="L3005" class="LineNr">3005 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3006" class="LineNr">3006 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3007" class="LineNr">3007 </span>  screen-should-contain [
+<span id="L3008" class="LineNr">3008 </span>   <span class="Constant"> .          .</span>
+<span id="L3009" class="LineNr">3009 </span>   <span class="Constant"> .a         .</span>
+<span id="L3010" class="LineNr">3010 </span>   <span class="Constant"> .b         .</span>
+<span id="L3011" class="LineNr">3011 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3012" class="LineNr">3012 </span>  ]
+<span id="L3013" class="LineNr">3013 </span>  <span class="Comment"># position cursor at last line, then try to move further down</span>
+<span id="L3014" class="LineNr">3014 </span>  assume-console [
+<span id="L3015" class="LineNr">3015 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<span id="L3016" class="LineNr">3016 </span>    press down-arrow
+<span id="L3017" class="LineNr">3017 </span>  ]
+<span id="L3018" class="LineNr">3018 </span>  run [
+<span id="L3019" class="LineNr">3019 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3020" class="LineNr">3020 </span>  ]
+<span id="L3021" class="LineNr">3021 </span>  <span class="Comment"># no change since the bottom border was already visible</span>
+<span id="L3022" class="LineNr">3022 </span>  screen-should-contain [
+<span id="L3023" class="LineNr">3023 </span>   <span class="Constant"> .          .</span>
+<span id="L3024" class="LineNr">3024 </span>   <span class="Constant"> .a         .</span>
+<span id="L3025" class="LineNr">3025 </span>   <span class="Constant"> .b         .</span>
+<span id="L3026" class="LineNr">3026 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3027" class="LineNr">3027 </span>  ]
 <span id="L3028" class="LineNr">3028 </span>]
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-<span id="L3030" class="LineNr">3030 </span>  run [
-<span id="L3031" class="LineNr">3031 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3032" class="LineNr">3032 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L3033" class="LineNr">3033 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
-<span id="L3034" class="LineNr">3034 </span>  ]
-<span id="L3035" class="LineNr">3035 </span>  <span class="Comment"># screen scrolls</span>
-<span id="L3036" class="LineNr">3036 </span>  screen-should-contain [
-<span id="L3037" class="LineNr">3037 </span>   <span class="Constant"> .     .</span>
-<span id="L3038" class="LineNr">3038 </span>   <span class="Constant"> .b    .</span>
-<span id="L3039" class="LineNr">3039 </span>   <span class="Constant"> .c    .</span>
-<span id="L3040" class="LineNr">3040 </span>   <span class="Constant"> .     .</span>
-<span id="L3041" class="LineNr">3041 </span>  ]
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-<span id="L3043" class="LineNr">3043 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-<span id="L3044" class="LineNr">3044 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
-<span id="L3045" class="LineNr">3045 </span>  ]
-<span id="L3046" class="LineNr">3046 </span>]
-<span id="L3047" class="LineNr">3047 </span>
-<span id="L3048" class="LineNr">3048 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-right-arrow [
-<span id="L3049" class="LineNr">3049 </span>  <span class="Constant">local-scope</span>
-<span id="L3050" class="LineNr">3050 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3051" class="LineNr">3051 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
-<span id="L3052" class="LineNr">3052 </span>  <span class="Comment"># editor contains a wrapped line</span>
-<span id="L3053" class="LineNr">3053 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3054" class="LineNr">3054 </span><span class="Constant">b</span>
-<span id="L3055" class="LineNr">3055 </span><span class="Constant">cdefgh]</span>
-<span id="L3056" class="LineNr">3056 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3057" class="LineNr">3057 </span>  <span class="Comment"># position cursor at end of screen and try to move right</span>
-<span id="L3058" class="LineNr">3058 </span>  assume-console [
-<span id="L3059" class="LineNr">3059 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 3</span>
-<span id="L3060" class="LineNr">3060 </span>    press right-arrow
-<span id="L3061" class="LineNr">3061 </span>  ]
-<span id="L3062" class="LineNr">3062 </span>  run [
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-<span id="L3064" class="LineNr">3064 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L3065" class="LineNr">3065 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
-<span id="L3066" class="LineNr">3066 </span>  ]
-<span id="L3067" class="LineNr">3067 </span>  <span class="Comment"># screen scrolls</span>
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-<span id="L3070" class="LineNr">3070 </span>   <span class="Constant"> .b    .</span>
-<span id="L3071" class="LineNr">3071 </span><span class="Constant">    .cdef↩.</span>
-<span id="L3072" class="LineNr">3072 </span>   <span class="Constant"> .gh   .</span>
-<span id="L3073" class="LineNr">3073 </span>  ]
-<span id="L3074" class="LineNr">3074 </span>  memory-should-contain [
-<span id="L3075" class="LineNr">3075 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-<span id="L3076" class="LineNr">3076 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
-<span id="L3077" class="LineNr">3077 </span>  ]
-<span id="L3078" class="LineNr">3078 </span>]
-<span id="L3079" class="LineNr">3079 </span>
-<span id="L3080" class="LineNr">3080 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-right-arrow-2 [
-<span id="L3081" class="LineNr">3081 </span>  <span class="Constant">local-scope</span>
-<span id="L3082" class="LineNr">3082 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3083" class="LineNr">3083 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
-<span id="L3084" class="LineNr">3084 </span>  <span class="Comment"># editor contains more lines than can fit on screen</span>
-<span id="L3085" class="LineNr">3085 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3086" class="LineNr">3086 </span><span class="Constant">b</span>
-<span id="L3087" class="LineNr">3087 </span><span class="Constant">c</span>
-<span id="L3088" class="LineNr">3088 </span><span class="Constant">d]</span>
-<span id="L3089" class="LineNr">3089 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3090" class="LineNr">3090 </span>  <span class="Comment"># position cursor at end of screen and try to move right</span>
-<span id="L3091" class="LineNr">3091 </span>  assume-console [
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-<span id="L3093" class="LineNr">3093 </span>    press right-arrow
-<span id="L3094" class="LineNr">3094 </span>  ]
-<span id="L3095" class="LineNr">3095 </span>  run [
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-<span id="L3098" class="LineNr">3098 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
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-<span id="L3104" class="LineNr">3104 </span>   <span class="Constant"> .c    .</span>
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-<span id="L3109" class="LineNr">3109 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
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-<span id="L3112" class="LineNr">3112 </span>
-<span id="L3113" class="LineNr">3113 </span><span class="muScenario">scenario</span> editor-scrolls-at-end-on-down-arrow [
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-<span id="L3119" class="LineNr">3119 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
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-<span id="L3126" class="LineNr">3126 </span>  run [
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-<span id="L3129" class="LineNr">3129 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
-<span id="L3130" class="LineNr">3130 </span>  ]
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-<span id="L3134" class="LineNr">3134 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
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-<span id="L3137" class="LineNr">3137 </span>
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-<span id="L3144" class="LineNr">3144 </span><span class="Constant">b</span>
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-<span id="L3149" class="LineNr">3149 </span><span class="Constant">g]</span>
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-<span id="L3179" class="LineNr">3179 </span><span class="Constant">c</span>
-<span id="L3180" class="LineNr">3180 </span><span class="Constant">d]</span>
-<span id="L3181" class="LineNr">3181 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3182" class="LineNr">3182 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3183" class="LineNr">3183 </span>  screen-should-contain [
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-<span id="L3185" class="LineNr">3185 </span>   <span class="Constant"> .a         .</span>
-<span id="L3186" class="LineNr">3186 </span>   <span class="Constant"> .b         .</span>
-<span id="L3187" class="LineNr">3187 </span>   <span class="Constant"> .c         .</span>
-<span id="L3188" class="LineNr">3188 </span>  ]
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-<span id="L3190" class="LineNr">3190 </span>  assume-console [
-<span id="L3191" class="LineNr">3191 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3192" class="LineNr">3192 </span>    press up-arrow
-<span id="L3193" class="LineNr">3193 </span>  ]
-<span id="L3194" class="LineNr">3194 </span>  run [
-<span id="L3195" class="LineNr">3195 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3196" class="LineNr">3196 </span>  ]
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-<span id="L3198" class="LineNr">3198 </span>  screen-should-contain [
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-<span id="L3200" class="LineNr">3200 </span>   <span class="Constant"> .b         .</span>
-<span id="L3201" class="LineNr">3201 </span>   <span class="Constant"> .c         .</span>
-<span id="L3202" class="LineNr">3202 </span>   <span class="Constant"> .d         .</span>
-<span id="L3203" class="LineNr">3203 </span>  ]
-<span id="L3204" class="LineNr">3204 </span>]
-<span id="L3205" class="LineNr">3205 </span>
-<span id="L3206" class="LineNr">3206 </span><span class="muRecipe">after</span> <span class="Constant">&lt;scroll-up&gt;</span> [
-<span id="L3207" class="LineNr">3207 </span>  trace<span class="Constant"> 10</span>, <span class="Constant">[app]</span>, <span class="Constant">[scroll up]</span>
-<span id="L3208" class="LineNr">3208 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3209" class="LineNr">3209 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy top-of-screen
-<span id="L3210" class="LineNr">3210 </span>  top-of-screen <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> top-of-screen, editor
-<span id="L3211" class="LineNr">3211 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
-<span id="L3212" class="LineNr">3212 </span>  no-movement?:bool <span class="Special">&lt;-</span> equal old-top, top-of-screen
-<span id="L3213" class="LineNr">3213 </span>  <span class="muControl">return-if</span> no-movement?, <span class="Constant">0/don't-render</span>
-<span id="L3214" class="LineNr">3214 </span>]
-<span id="L3215" class="LineNr">3215 </span>
-<span id="L3216" class="LineNr">3216 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys [
-<span id="L3217" class="LineNr">3217 </span>  <span class="Constant">local-scope</span>
-<span id="L3218" class="LineNr">3218 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3219" class="LineNr">3219 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3220" class="LineNr">3220 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
-<span id="L3221" class="LineNr">3221 </span>  <span class="Comment"># other lines</span>
-<span id="L3222" class="LineNr">3222 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
-<span id="L3223" class="LineNr">3223 </span><span class="Constant">g</span>
-<span id="L3224" class="LineNr">3224 </span><span class="Constant">h</span>
-<span id="L3225" class="LineNr">3225 </span><span class="Constant">i]</span>
-<span id="L3226" class="LineNr">3226 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3227" class="LineNr">3227 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3228" class="LineNr">3228 </span>  screen-should-contain [
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-<span id="L3232" class="LineNr">3232 </span>   <span class="Constant"> .g         .</span>
-<span id="L3233" class="LineNr">3233 </span>  ]
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-<span id="L3235" class="LineNr">3235 </span>  assume-console [
-<span id="L3236" class="LineNr">3236 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3237" class="LineNr">3237 </span>  ]
-<span id="L3238" class="LineNr">3238 </span>  run [
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-<span id="L3240" class="LineNr">3240 </span>  ]
+<span id="L3029" class="LineNr">3029 </span>
+<span id="L3030" class="LineNr">3030 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-newline [
+<span id="L3031" class="LineNr">3031 </span>  <span class="Constant">local-scope</span>
+<span id="L3032" class="LineNr">3032 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
+<span id="L3033" class="LineNr">3033 </span>  <span class="Comment"># position cursor after last line and type newline</span>
+<span id="L3034" class="LineNr">3034 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3035" class="LineNr">3035 </span><span class="Constant">b</span>
+<span id="L3036" class="LineNr">3036 </span><span class="Constant">c]</span>
+<span id="L3037" class="LineNr">3037 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3038" class="LineNr">3038 </span>  assume-console [
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+<span id="L3040" class="LineNr">3040 </span>    type [
+<span id="L3041" class="LineNr">3041 </span>]
+<span id="L3042" class="LineNr">3042 </span>  ]
+<span id="L3043" class="LineNr">3043 </span>  run [
+<span id="L3044" class="LineNr">3044 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3045" class="LineNr">3045 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L3046" class="LineNr">3046 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L3047" class="LineNr">3047 </span>  ]
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+<span id="L3052" class="LineNr">3052 </span>   <span class="Constant"> .c    .</span>
+<span id="L3053" class="LineNr">3053 </span>   <span class="Constant"> .     .</span>
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+<span id="L3056" class="LineNr">3056 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<span id="L3057" class="LineNr">3057 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L3058" class="LineNr">3058 </span>  ]
+<span id="L3059" class="LineNr">3059 </span>]
+<span id="L3060" class="LineNr">3060 </span>
+<span id="L3061" class="LineNr">3061 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-right-arrow [
+<span id="L3062" class="LineNr">3062 </span>  <span class="Constant">local-scope</span>
+<span id="L3063" class="LineNr">3063 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3064" class="LineNr">3064 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
+<span id="L3065" class="LineNr">3065 </span>  <span class="Comment"># editor contains a wrapped line</span>
+<span id="L3066" class="LineNr">3066 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3067" class="LineNr">3067 </span><span class="Constant">b</span>
+<span id="L3068" class="LineNr">3068 </span><span class="Constant">cdefgh]</span>
+<span id="L3069" class="LineNr">3069 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3070" class="LineNr">3070 </span>  <span class="Comment"># position cursor at end of screen and try to move right</span>
+<span id="L3071" class="LineNr">3071 </span>  assume-console [
+<span id="L3072" class="LineNr">3072 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 3</span>
+<span id="L3073" class="LineNr">3073 </span>    press right-arrow
+<span id="L3074" class="LineNr">3074 </span>  ]
+<span id="L3075" class="LineNr">3075 </span>  run [
+<span id="L3076" class="LineNr">3076 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3077" class="LineNr">3077 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L3078" class="LineNr">3078 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
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+<span id="L3080" class="LineNr">3080 </span>  <span class="Comment"># screen scrolls</span>
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+<span id="L3082" class="LineNr">3082 </span>   <span class="Constant"> .     .</span>
+<span id="L3083" class="LineNr">3083 </span>   <span class="Constant"> .b    .</span>
+<span id="L3084" class="LineNr">3084 </span><span class="Constant">    .cdef↩.</span>
+<span id="L3085" class="LineNr">3085 </span>   <span class="Constant"> .gh   .</span>
+<span id="L3086" class="LineNr">3086 </span>  ]
+<span id="L3087" class="LineNr">3087 </span>  memory-should-contain [
+<span id="L3088" class="LineNr">3088 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
+<span id="L3089" class="LineNr">3089 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L3090" class="LineNr">3090 </span>  ]
+<span id="L3091" class="LineNr">3091 </span>]
+<span id="L3092" class="LineNr">3092 </span>
+<span id="L3093" class="LineNr">3093 </span><span class="muScenario">scenario</span> editor-scrolls-down-on-right-arrow-2 [
+<span id="L3094" class="LineNr">3094 </span>  <span class="Constant">local-scope</span>
+<span id="L3095" class="LineNr">3095 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3096" class="LineNr">3096 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
+<span id="L3097" class="LineNr">3097 </span>  <span class="Comment"># editor contains more lines than can fit on screen</span>
+<span id="L3098" class="LineNr">3098 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3099" class="LineNr">3099 </span><span class="Constant">b</span>
+<span id="L3100" class="LineNr">3100 </span><span class="Constant">c</span>
+<span id="L3101" class="LineNr">3101 </span><span class="Constant">d]</span>
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+<span id="L3103" class="LineNr">3103 </span>  <span class="Comment"># position cursor at end of screen and try to move right</span>
+<span id="L3104" class="LineNr">3104 </span>  assume-console [
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+<span id="L3106" class="LineNr">3106 </span>    press right-arrow
+<span id="L3107" class="LineNr">3107 </span>  ]
+<span id="L3108" class="LineNr">3108 </span>  run [
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+<span id="L3110" class="LineNr">3110 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L3111" class="LineNr">3111 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
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+<span id="L3122" class="LineNr">3122 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L3123" class="LineNr">3123 </span>  ]
+<span id="L3124" class="LineNr">3124 </span>]
+<span id="L3125" class="LineNr">3125 </span>
+<span id="L3126" class="LineNr">3126 </span><span class="muScenario">scenario</span> editor-scrolls-at-end-on-down-arrow [
+<span id="L3127" class="LineNr">3127 </span>  <span class="Constant">local-scope</span>
+<span id="L3128" class="LineNr">3128 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
+<span id="L3129" class="LineNr">3129 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
+<span id="L3130" class="LineNr">3130 </span><span class="Constant">de]</span>
+<span id="L3131" class="LineNr">3131 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3132" class="LineNr">3132 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3133" class="LineNr">3133 </span>  $clear-trace
+<span id="L3134" class="LineNr">3134 </span>  <span class="Comment"># try to move down past end of text</span>
+<span id="L3135" class="LineNr">3135 </span>  assume-console [
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+<span id="L3137" class="LineNr">3137 </span>    press down-arrow
+<span id="L3138" class="LineNr">3138 </span>  ]
+<span id="L3139" class="LineNr">3139 </span>  run [
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+<span id="L3141" class="LineNr">3141 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L3142" class="LineNr">3142 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L3143" class="LineNr">3143 </span>  ]
+<span id="L3144" class="LineNr">3144 </span>  <span class="Comment"># no change</span>
+<span id="L3145" class="LineNr">3145 </span>  memory-should-contain [
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+<span id="L3147" class="LineNr">3147 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 0</span>
+<span id="L3148" class="LineNr">3148 </span>  ]
+<span id="L3149" class="LineNr">3149 </span>]
+<span id="L3150" class="LineNr">3150 </span>
+<span id="L3151" class="LineNr">3151 </span><span class="muScenario">scenario</span> editor-combines-page-and-line-scroll [
+<span id="L3152" class="LineNr">3152 </span>  <span class="Constant">local-scope</span>
+<span id="L3153" class="LineNr">3153 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3154" class="LineNr">3154 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3155" class="LineNr">3155 </span>  <span class="Comment"># initialize editor with a few pages of lines</span>
+<span id="L3156" class="LineNr">3156 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3157" class="LineNr">3157 </span><span class="Constant">b</span>
+<span id="L3158" class="LineNr">3158 </span><span class="Constant">c</span>
+<span id="L3159" class="LineNr">3159 </span><span class="Constant">d</span>
+<span id="L3160" class="LineNr">3160 </span><span class="Constant">e</span>
+<span id="L3161" class="LineNr">3161 </span><span class="Constant">f</span>
+<span id="L3162" class="LineNr">3162 </span><span class="Constant">g]</span>
+<span id="L3163" class="LineNr">3163 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3164" class="LineNr">3164 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3165" class="LineNr">3165 </span>  <span class="Comment"># scroll down one page and one line</span>
+<span id="L3166" class="LineNr">3166 </span>  assume-console [
+<span id="L3167" class="LineNr">3167 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3168" class="LineNr">3168 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 0</span>
+<span id="L3169" class="LineNr">3169 </span>    press down-arrow
+<span id="L3170" class="LineNr">3170 </span>  ]
+<span id="L3171" class="LineNr">3171 </span>  run [
+<span id="L3172" class="LineNr">3172 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3173" class="LineNr">3173 </span>  ]
+<span id="L3174" class="LineNr">3174 </span>  <span class="Comment"># screen scrolls down 3 lines</span>
+<span id="L3175" class="LineNr">3175 </span>  screen-should-contain [
+<span id="L3176" class="LineNr">3176 </span>   <span class="Constant"> .          .</span>
+<span id="L3177" class="LineNr">3177 </span>   <span class="Constant"> .d         .</span>
+<span id="L3178" class="LineNr">3178 </span>   <span class="Constant"> .e         .</span>
+<span id="L3179" class="LineNr">3179 </span>   <span class="Constant"> .f         .</span>
+<span id="L3180" class="LineNr">3180 </span>  ]
+<span id="L3181" class="LineNr">3181 </span>]
+<span id="L3182" class="LineNr">3182 </span>
+<span id="L3183" class="LineNr">3183 </span><span class="Comment"># scroll up if necessary</span>
+<span id="L3184" class="LineNr">3184 </span>
+<span id="L3185" class="LineNr">3185 </span><span class="muScenario">scenario</span> editor-can-scroll-up-using-arrow-keys [
+<span id="L3186" class="LineNr">3186 </span>  <span class="Constant">local-scope</span>
+<span id="L3187" class="LineNr">3187 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3188" class="LineNr">3188 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3189" class="LineNr">3189 </span>  <span class="Comment"># initialize editor with &gt;3 lines</span>
+<span id="L3190" class="LineNr">3190 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3191" class="LineNr">3191 </span><span class="Constant">b</span>
+<span id="L3192" class="LineNr">3192 </span><span class="Constant">c</span>
+<span id="L3193" class="LineNr">3193 </span><span class="Constant">d]</span>
+<span id="L3194" class="LineNr">3194 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3195" class="LineNr">3195 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3196" class="LineNr">3196 </span>  screen-should-contain [
+<span id="L3197" class="LineNr">3197 </span>   <span class="Constant"> .          .</span>
+<span id="L3198" class="LineNr">3198 </span>   <span class="Constant"> .a         .</span>
+<span id="L3199" class="LineNr">3199 </span>   <span class="Constant"> .b         .</span>
+<span id="L3200" class="LineNr">3200 </span>   <span class="Constant"> .c         .</span>
+<span id="L3201" class="LineNr">3201 </span>  ]
+<span id="L3202" class="LineNr">3202 </span>  <span class="Comment"># position cursor at top of second page, then try to move up</span>
+<span id="L3203" class="LineNr">3203 </span>  assume-console [
+<span id="L3204" class="LineNr">3204 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3205" class="LineNr">3205 </span>    press up-arrow
+<span id="L3206" class="LineNr">3206 </span>  ]
+<span id="L3207" class="LineNr">3207 </span>  run [
+<span id="L3208" class="LineNr">3208 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3209" class="LineNr">3209 </span>  ]
+<span id="L3210" class="LineNr">3210 </span>  <span class="Comment"># screen slides by one line</span>
+<span id="L3211" class="LineNr">3211 </span>  screen-should-contain [
+<span id="L3212" class="LineNr">3212 </span>   <span class="Constant"> .          .</span>
+<span id="L3213" class="LineNr">3213 </span>   <span class="Constant"> .b         .</span>
+<span id="L3214" class="LineNr">3214 </span>   <span class="Constant"> .c         .</span>
+<span id="L3215" class="LineNr">3215 </span>   <span class="Constant"> .d         .</span>
+<span id="L3216" class="LineNr">3216 </span>  ]
+<span id="L3217" class="LineNr">3217 </span>]
+<span id="L3218" class="LineNr">3218 </span>
+<span id="L3219" class="LineNr">3219 </span><span class="muRecipe">after</span> <span class="Constant">&lt;scroll-up&gt;</span> [
+<span id="L3220" class="LineNr">3220 </span>  trace<span class="Constant"> 10</span>, <span class="Constant">[app]</span>, <span class="Constant">[scroll up]</span>
+<span id="L3221" class="LineNr">3221 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3222" class="LineNr">3222 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy top-of-screen
+<span id="L3223" class="LineNr">3223 </span>  top-of-screen <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> top-of-screen, editor
+<span id="L3224" class="LineNr">3224 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
+<span id="L3225" class="LineNr">3225 </span>  no-movement?:bool <span class="Special">&lt;-</span> equal old-top, top-of-screen
+<span id="L3226" class="LineNr">3226 </span>  <span class="muControl">return-if</span> no-movement?,<span class="Constant"> false/don't-render</span>
+<span id="L3227" class="LineNr">3227 </span>]
+<span id="L3228" class="LineNr">3228 </span>
+<span id="L3229" class="LineNr">3229 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys [
+<span id="L3230" class="LineNr">3230 </span>  <span class="Constant">local-scope</span>
+<span id="L3231" class="LineNr">3231 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3232" class="LineNr">3232 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3233" class="LineNr">3233 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
+<span id="L3234" class="LineNr">3234 </span>  <span class="Comment"># other lines</span>
+<span id="L3235" class="LineNr">3235 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
+<span id="L3236" class="LineNr">3236 </span><span class="Constant">g</span>
+<span id="L3237" class="LineNr">3237 </span><span class="Constant">h</span>
+<span id="L3238" class="LineNr">3238 </span><span class="Constant">i]</span>
+<span id="L3239" class="LineNr">3239 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3240" class="LineNr">3240 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L3241" class="LineNr">3241 </span>  screen-should-contain [
 <span id="L3242" class="LineNr">3242 </span>   <span class="Constant"> .          .</span>
-<span id="L3243" class="LineNr">3243 </span>   <span class="Constant"> .g         .</span>
-<span id="L3244" class="LineNr">3244 </span>   <span class="Constant"> .h         .</span>
-<span id="L3245" class="LineNr">3245 </span>   <span class="Constant"> .i         .</span>
+<span id="L3243" class="LineNr">3243 </span>   <span class="Constant"> .abcd↩     .</span>
+<span id="L3244" class="LineNr">3244 </span>   <span class="Constant"> .ef        .</span>
+<span id="L3245" class="LineNr">3245 </span>   <span class="Constant"> .g         .</span>
 <span id="L3246" class="LineNr">3246 </span>  ]
-<span id="L3247" class="LineNr">3247 </span>  <span class="Comment"># now move up one line</span>
+<span id="L3247" class="LineNr">3247 </span>  <span class="Comment"># position cursor at top of second page, just below wrapped line</span>
 <span id="L3248" class="LineNr">3248 </span>  assume-console [
-<span id="L3249" class="LineNr">3249 </span>    press up-arrow
+<span id="L3249" class="LineNr">3249 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L3250" class="LineNr">3250 </span>  ]
 <span id="L3251" class="LineNr">3251 </span>  run [
 <span id="L3252" class="LineNr">3252 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L3253" class="LineNr">3253 </span>  ]
-<span id="L3254" class="LineNr">3254 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L3255" class="LineNr">3255 </span>  screen-should-contain [
-<span id="L3256" class="LineNr">3256 </span>   <span class="Constant"> .          .</span>
-<span id="L3257" class="LineNr">3257 </span>   <span class="Constant"> .ef        .</span>
-<span id="L3258" class="LineNr">3258 </span>   <span class="Constant"> .g         .</span>
-<span id="L3259" class="LineNr">3259 </span>   <span class="Constant"> .h         .</span>
-<span id="L3260" class="LineNr">3260 </span>  ]
-<span id="L3261" class="LineNr">3261 </span>]
-<span id="L3262" class="LineNr">3262 </span>
-<span id="L3263" class="LineNr">3263 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-2 [
-<span id="L3264" class="LineNr">3264 </span>  <span class="Constant">local-scope</span>
-<span id="L3265" class="LineNr">3265 </span>  <span class="Comment"># screen has 1 line for menu + 4 lines</span>
-<span id="L3266" class="LineNr">3266 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
-<span id="L3267" class="LineNr">3267 </span>  <span class="Comment"># editor starts with a long line wrapping twice, occupying 3 of the 4 lines</span>
-<span id="L3268" class="LineNr">3268 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdefghij</span>
-<span id="L3269" class="LineNr">3269 </span><span class="Constant">k</span>
-<span id="L3270" class="LineNr">3270 </span><span class="Constant">l</span>
-<span id="L3271" class="LineNr">3271 </span><span class="Constant">m]</span>
-<span id="L3272" class="LineNr">3272 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3273" class="LineNr">3273 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3274" class="LineNr">3274 </span>  <span class="Comment"># position cursor at top of second page</span>
-<span id="L3275" class="LineNr">3275 </span>  assume-console [
-<span id="L3276" class="LineNr">3276 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3277" class="LineNr">3277 </span>  ]
-<span id="L3278" class="LineNr">3278 </span>  run [
-<span id="L3279" class="LineNr">3279 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3280" class="LineNr">3280 </span>  ]
-<span id="L3281" class="LineNr">3281 </span>  screen-should-contain [
-<span id="L3282" class="LineNr">3282 </span>   <span class="Constant"> .          .</span>
-<span id="L3283" class="LineNr">3283 </span>   <span class="Constant"> .k         .</span>
-<span id="L3284" class="LineNr">3284 </span>   <span class="Constant"> .l         .</span>
-<span id="L3285" class="LineNr">3285 </span>   <span class="Constant"> .m         .</span>
-<span id="L3286" class="LineNr">3286 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
-<span id="L3287" class="LineNr">3287 </span>  ]
-<span id="L3288" class="LineNr">3288 </span>  <span class="Comment"># move up one line</span>
-<span id="L3289" class="LineNr">3289 </span>  assume-console [
-<span id="L3290" class="LineNr">3290 </span>    press up-arrow
-<span id="L3291" class="LineNr">3291 </span>  ]
-<span id="L3292" class="LineNr">3292 </span>  run [
-<span id="L3293" class="LineNr">3293 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3294" class="LineNr">3294 </span>  ]
-<span id="L3295" class="LineNr">3295 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L3296" class="LineNr">3296 </span>  screen-should-contain [
-<span id="L3297" class="LineNr">3297 </span>   <span class="Constant"> .          .</span>
-<span id="L3298" class="LineNr">3298 </span>   <span class="Constant"> .ij        .</span>
-<span id="L3299" class="LineNr">3299 </span>   <span class="Constant"> .k         .</span>
-<span id="L3300" class="LineNr">3300 </span>   <span class="Constant"> .l         .</span>
-<span id="L3301" class="LineNr">3301 </span>   <span class="Constant"> .m         .</span>
-<span id="L3302" class="LineNr">3302 </span>  ]
-<span id="L3303" class="LineNr">3303 </span>  <span class="Comment"># move up a second line</span>
-<span id="L3304" class="LineNr">3304 </span>  assume-console [
-<span id="L3305" class="LineNr">3305 </span>    press up-arrow
-<span id="L3306" class="LineNr">3306 </span>  ]
-<span id="L3307" class="LineNr">3307 </span>  run [
-<span id="L3308" class="LineNr">3308 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3309" class="LineNr">3309 </span>  ]
-<span id="L3310" class="LineNr">3310 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L3311" class="LineNr">3311 </span>  screen-should-contain [
-<span id="L3312" class="LineNr">3312 </span>   <span class="Constant"> .          .</span>
-<span id="L3313" class="LineNr">3313 </span>   <span class="Constant"> .efgh↩     .</span>
-<span id="L3314" class="LineNr">3314 </span>   <span class="Constant"> .ij        .</span>
-<span id="L3315" class="LineNr">3315 </span>   <span class="Constant"> .k         .</span>
-<span id="L3316" class="LineNr">3316 </span>   <span class="Constant"> .l         .</span>
-<span id="L3317" class="LineNr">3317 </span>  ]
-<span id="L3318" class="LineNr">3318 </span>  <span class="Comment"># move up a third line</span>
-<span id="L3319" class="LineNr">3319 </span>  assume-console [
-<span id="L3320" class="LineNr">3320 </span>    press up-arrow
-<span id="L3321" class="LineNr">3321 </span>  ]
-<span id="L3322" class="LineNr">3322 </span>  run [
-<span id="L3323" class="LineNr">3323 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3324" class="LineNr">3324 </span>  ]
-<span id="L3325" class="LineNr">3325 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L3326" class="LineNr">3326 </span>  screen-should-contain [
-<span id="L3327" class="LineNr">3327 </span>   <span class="Constant"> .          .</span>
-<span id="L3328" class="LineNr">3328 </span>   <span class="Constant"> .abcd↩     .</span>
-<span id="L3329" class="LineNr">3329 </span>   <span class="Constant"> .efgh↩     .</span>
-<span id="L3330" class="LineNr">3330 </span>   <span class="Constant"> .ij        .</span>
-<span id="L3331" class="LineNr">3331 </span>   <span class="Constant"> .k         .</span>
-<span id="L3332" class="LineNr">3332 </span>  ]
-<span id="L3333" class="LineNr">3333 </span>]
-<span id="L3334" class="LineNr">3334 </span>
-<span id="L3335" class="LineNr">3335 </span><span class="Comment"># same as editor-scrolls-up-past-wrapped-line-using-arrow-keys but length</span>
-<span id="L3336" class="LineNr">3336 </span><span class="Comment"># slightly off, just to prevent over-training</span>
-<span id="L3337" class="LineNr">3337 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-3 [
-<span id="L3338" class="LineNr">3338 </span>  <span class="Constant">local-scope</span>
-<span id="L3339" class="LineNr">3339 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3340" class="LineNr">3340 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3341" class="LineNr">3341 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
-<span id="L3342" class="LineNr">3342 </span>  <span class="Comment"># other lines</span>
-<span id="L3343" class="LineNr">3343 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
-<span id="L3344" class="LineNr">3344 </span><span class="Constant">g</span>
-<span id="L3345" class="LineNr">3345 </span><span class="Constant">h</span>
-<span id="L3346" class="LineNr">3346 </span><span class="Constant">i]</span>
-<span id="L3347" class="LineNr">3347 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">6/right</span>
-<span id="L3348" class="LineNr">3348 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3349" class="LineNr">3349 </span>  screen-should-contain [
-<span id="L3350" class="LineNr">3350 </span>   <span class="Constant"> .          .</span>
-<span id="L3351" class="LineNr">3351 </span>   <span class="Constant"> .abcde↩    .</span>
-<span id="L3352" class="LineNr">3352 </span>   <span class="Constant"> .f         .</span>
-<span id="L3353" class="LineNr">3353 </span>   <span class="Constant"> .g         .</span>
-<span id="L3354" class="LineNr">3354 </span>  ]
-<span id="L3355" class="LineNr">3355 </span>  <span class="Comment"># position cursor at top of second page, just below wrapped line</span>
-<span id="L3356" class="LineNr">3356 </span>  assume-console [
-<span id="L3357" class="LineNr">3357 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3358" class="LineNr">3358 </span>  ]
-<span id="L3359" class="LineNr">3359 </span>  run [
-<span id="L3360" class="LineNr">3360 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3361" class="LineNr">3361 </span>  ]
+<span id="L3254" class="LineNr">3254 </span>  screen-should-contain [
+<span id="L3255" class="LineNr">3255 </span>   <span class="Constant"> .          .</span>
+<span id="L3256" class="LineNr">3256 </span>   <span class="Constant"> .g         .</span>
+<span id="L3257" class="LineNr">3257 </span>   <span class="Constant"> .h         .</span>
+<span id="L3258" class="LineNr">3258 </span>   <span class="Constant"> .i         .</span>
+<span id="L3259" class="LineNr">3259 </span>  ]
+<span id="L3260" class="LineNr">3260 </span>  <span class="Comment"># now move up one line</span>
+<span id="L3261" class="LineNr">3261 </span>  assume-console [
+<span id="L3262" class="LineNr">3262 </span>    press up-arrow
+<span id="L3263" class="LineNr">3263 </span>  ]
+<span id="L3264" class="LineNr">3264 </span>  run [
+<span id="L3265" class="LineNr">3265 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3266" class="LineNr">3266 </span>  ]
+<span id="L3267" class="LineNr">3267 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L3268" class="LineNr">3268 </span>  screen-should-contain [
+<span id="L3269" class="LineNr">3269 </span>   <span class="Constant"> .          .</span>
+<span id="L3270" class="LineNr">3270 </span>   <span class="Constant"> .ef        .</span>
+<span id="L3271" class="LineNr">3271 </span>   <span class="Constant"> .g         .</span>
+<span id="L3272" class="LineNr">3272 </span>   <span class="Constant"> .h         .</span>
+<span id="L3273" class="LineNr">3273 </span>  ]
+<span id="L3274" class="LineNr">3274 </span>]
+<span id="L3275" class="LineNr">3275 </span>
+<span id="L3276" class="LineNr">3276 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-2 [
+<span id="L3277" class="LineNr">3277 </span>  <span class="Constant">local-scope</span>
+<span id="L3278" class="LineNr">3278 </span>  <span class="Comment"># screen has 1 line for menu + 4 lines</span>
+<span id="L3279" class="LineNr">3279 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
+<span id="L3280" class="LineNr">3280 </span>  <span class="Comment"># editor starts with a long line wrapping twice, occupying 3 of the 4 lines</span>
+<span id="L3281" class="LineNr">3281 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdefghij</span>
+<span id="L3282" class="LineNr">3282 </span><span class="Constant">k</span>
+<span id="L3283" class="LineNr">3283 </span><span class="Constant">l</span>
+<span id="L3284" class="LineNr">3284 </span><span class="Constant">m]</span>
+<span id="L3285" class="LineNr">3285 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3286" class="LineNr">3286 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3287" class="LineNr">3287 </span>  <span class="Comment"># position cursor at top of second page</span>
+<span id="L3288" class="LineNr">3288 </span>  assume-console [
+<span id="L3289" class="LineNr">3289 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3290" class="LineNr">3290 </span>  ]
+<span id="L3291" class="LineNr">3291 </span>  run [
+<span id="L3292" class="LineNr">3292 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3293" class="LineNr">3293 </span>  ]
+<span id="L3294" class="LineNr">3294 </span>  screen-should-contain [
+<span id="L3295" class="LineNr">3295 </span>   <span class="Constant"> .          .</span>
+<span id="L3296" class="LineNr">3296 </span>   <span class="Constant"> .k         .</span>
+<span id="L3297" class="LineNr">3297 </span>   <span class="Constant"> .l         .</span>
+<span id="L3298" class="LineNr">3298 </span>   <span class="Constant"> .m         .</span>
+<span id="L3299" class="LineNr">3299 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
+<span id="L3300" class="LineNr">3300 </span>  ]
+<span id="L3301" class="LineNr">3301 </span>  <span class="Comment"># move up one line</span>
+<span id="L3302" class="LineNr">3302 </span>  assume-console [
+<span id="L3303" class="LineNr">3303 </span>    press up-arrow
+<span id="L3304" class="LineNr">3304 </span>  ]
+<span id="L3305" class="LineNr">3305 </span>  run [
+<span id="L3306" class="LineNr">3306 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3307" class="LineNr">3307 </span>  ]
+<span id="L3308" class="LineNr">3308 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L3309" class="LineNr">3309 </span>  screen-should-contain [
+<span id="L3310" class="LineNr">3310 </span>   <span class="Constant"> .          .</span>
+<span id="L3311" class="LineNr">3311 </span>   <span class="Constant"> .ij        .</span>
+<span id="L3312" class="LineNr">3312 </span>   <span class="Constant"> .k         .</span>
+<span id="L3313" class="LineNr">3313 </span>   <span class="Constant"> .l         .</span>
+<span id="L3314" class="LineNr">3314 </span>   <span class="Constant"> .m         .</span>
+<span id="L3315" class="LineNr">3315 </span>  ]
+<span id="L3316" class="LineNr">3316 </span>  <span class="Comment"># move up a second line</span>
+<span id="L3317" class="LineNr">3317 </span>  assume-console [
+<span id="L3318" class="LineNr">3318 </span>    press up-arrow
+<span id="L3319" class="LineNr">3319 </span>  ]
+<span id="L3320" class="LineNr">3320 </span>  run [
+<span id="L3321" class="LineNr">3321 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3322" class="LineNr">3322 </span>  ]
+<span id="L3323" class="LineNr">3323 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L3324" class="LineNr">3324 </span>  screen-should-contain [
+<span id="L3325" class="LineNr">3325 </span>   <span class="Constant"> .          .</span>
+<span id="L3326" class="LineNr">3326 </span>   <span class="Constant"> .efgh↩     .</span>
+<span id="L3327" class="LineNr">3327 </span>   <span class="Constant"> .ij        .</span>
+<span id="L3328" class="LineNr">3328 </span>   <span class="Constant"> .k         .</span>
+<span id="L3329" class="LineNr">3329 </span>   <span class="Constant"> .l         .</span>
+<span id="L3330" class="LineNr">3330 </span>  ]
+<span id="L3331" class="LineNr">3331 </span>  <span class="Comment"># move up a third line</span>
+<span id="L3332" class="LineNr">3332 </span>  assume-console [
+<span id="L3333" class="LineNr">3333 </span>    press up-arrow
+<span id="L3334" class="LineNr">3334 </span>  ]
+<span id="L3335" class="LineNr">3335 </span>  run [
+<span id="L3336" class="LineNr">3336 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3337" class="LineNr">3337 </span>  ]
+<span id="L3338" class="LineNr">3338 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L3339" class="LineNr">3339 </span>  screen-should-contain [
+<span id="L3340" class="LineNr">3340 </span>   <span class="Constant"> .          .</span>
+<span id="L3341" class="LineNr">3341 </span>   <span class="Constant"> .abcd↩     .</span>
+<span id="L3342" class="LineNr">3342 </span>   <span class="Constant"> .efgh↩     .</span>
+<span id="L3343" class="LineNr">3343 </span>   <span class="Constant"> .ij        .</span>
+<span id="L3344" class="LineNr">3344 </span>   <span class="Constant"> .k         .</span>
+<span id="L3345" class="LineNr">3345 </span>  ]
+<span id="L3346" class="LineNr">3346 </span>]
+<span id="L3347" class="LineNr">3347 </span>
+<span id="L3348" class="LineNr">3348 </span><span class="Comment"># same as editor-scrolls-up-past-wrapped-line-using-arrow-keys but length</span>
+<span id="L3349" class="LineNr">3349 </span><span class="Comment"># slightly off, just to prevent over-training</span>
+<span id="L3350" class="LineNr">3350 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-3 [
+<span id="L3351" class="LineNr">3351 </span>  <span class="Constant">local-scope</span>
+<span id="L3352" class="LineNr">3352 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3353" class="LineNr">3353 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3354" class="LineNr">3354 </span>  <span class="Comment"># initialize editor with a long, wrapped line and more than a screen of</span>
+<span id="L3355" class="LineNr">3355 </span>  <span class="Comment"># other lines</span>
+<span id="L3356" class="LineNr">3356 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[abcdef</span>
+<span id="L3357" class="LineNr">3357 </span><span class="Constant">g</span>
+<span id="L3358" class="LineNr">3358 </span><span class="Constant">h</span>
+<span id="L3359" class="LineNr">3359 </span><span class="Constant">i]</span>
+<span id="L3360" class="LineNr">3360 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">6/right</span>
+<span id="L3361" class="LineNr">3361 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L3362" class="LineNr">3362 </span>  screen-should-contain [
 <span id="L3363" class="LineNr">3363 </span>   <span class="Constant"> .          .</span>
-<span id="L3364" class="LineNr">3364 </span>   <span class="Constant"> .g         .</span>
-<span id="L3365" class="LineNr">3365 </span>   <span class="Constant"> .h         .</span>
-<span id="L3366" class="LineNr">3366 </span>   <span class="Constant"> .i         .</span>
+<span id="L3364" class="LineNr">3364 </span>   <span class="Constant"> .abcde↩    .</span>
+<span id="L3365" class="LineNr">3365 </span>   <span class="Constant"> .f         .</span>
+<span id="L3366" class="LineNr">3366 </span>   <span class="Constant"> .g         .</span>
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-<span id="L3368" class="LineNr">3368 </span>  <span class="Comment"># now move up one line</span>
+<span id="L3368" class="LineNr">3368 </span>  <span class="Comment"># position cursor at top of second page, just below wrapped line</span>
 <span id="L3369" class="LineNr">3369 </span>  assume-console [
-<span id="L3370" class="LineNr">3370 </span>    press up-arrow
+<span id="L3370" class="LineNr">3370 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L3371" class="LineNr">3371 </span>  ]
 <span id="L3372" class="LineNr">3372 </span>  run [
 <span id="L3373" class="LineNr">3373 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L3374" class="LineNr">3374 </span>  ]
-<span id="L3375" class="LineNr">3375 </span>  <span class="Comment"># screen shows partial wrapped line</span>
-<span id="L3376" class="LineNr">3376 </span>  screen-should-contain [
-<span id="L3377" class="LineNr">3377 </span>   <span class="Constant"> .          .</span>
-<span id="L3378" class="LineNr">3378 </span>   <span class="Constant"> .f         .</span>
-<span id="L3379" class="LineNr">3379 </span>   <span class="Constant"> .g         .</span>
-<span id="L3380" class="LineNr">3380 </span>   <span class="Constant"> .h         .</span>
-<span id="L3381" class="LineNr">3381 </span>  ]
-<span id="L3382" class="LineNr">3382 </span>]
-<span id="L3383" class="LineNr">3383 </span>
-<span id="L3384" class="LineNr">3384 </span><span class="Comment"># check empty lines</span>
-<span id="L3385" class="LineNr">3385 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-4 [
-<span id="L3386" class="LineNr">3386 </span>  <span class="Constant">local-scope</span>
-<span id="L3387" class="LineNr">3387 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3388" class="LineNr">3388 </span>  <span class="Comment"># initialize editor with some lines around an empty line</span>
-<span id="L3389" class="LineNr">3389 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3390" class="LineNr">3390 </span><span class="Constant">b</span>
-<span id="L3391" class="LineNr">3391 </span>
-<span id="L3392" class="LineNr">3392 </span>c
-<span id="L3393" class="LineNr">3393 </span>d
-<span id="L3394" class="LineNr">3394 </span>e]
-<span id="L3395" class="LineNr">3395 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">6/right</span>
-<span id="L3396" class="LineNr">3396 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3397" class="LineNr">3397 </span>  assume-console [
-<span id="L3398" class="LineNr">3398 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3399" class="LineNr">3399 </span>  ]
-<span id="L3400" class="LineNr">3400 </span>  run [
-<span id="L3401" class="LineNr">3401 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3402" class="LineNr">3402 </span>  ]
-<span id="L3403" class="LineNr">3403 </span>  screen-should-contain [
-<span id="L3404" class="LineNr">3404 </span>   <span class="Constant"> .          .</span>
-<span id="L3405" class="LineNr">3405 </span>   <span class="Constant"> .          .</span>
-<span id="L3406" class="LineNr">3406 </span>   <span class="Constant"> .c         .</span>
-<span id="L3407" class="LineNr">3407 </span>   <span class="Constant"> .d         .</span>
-<span id="L3408" class="LineNr">3408 </span>  ]
-<span id="L3409" class="LineNr">3409 </span>  assume-console [
-<span id="L3410" class="LineNr">3410 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3411" class="LineNr">3411 </span>  ]
-<span id="L3412" class="LineNr">3412 </span>  run [
-<span id="L3413" class="LineNr">3413 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3414" class="LineNr">3414 </span>  ]
-<span id="L3415" class="LineNr">3415 </span>  screen-should-contain [
-<span id="L3416" class="LineNr">3416 </span>   <span class="Constant"> .          .</span>
-<span id="L3417" class="LineNr">3417 </span>   <span class="Constant"> .d         .</span>
-<span id="L3418" class="LineNr">3418 </span>   <span class="Constant"> .e         .</span>
-<span id="L3419" class="LineNr">3419 </span>   <span class="Constant"> .╌╌╌╌╌╌    .</span>
-<span id="L3420" class="LineNr">3420 </span>  ]
-<span id="L3421" class="LineNr">3421 </span>  assume-console [
-<span id="L3422" class="LineNr">3422 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
-<span id="L3423" class="LineNr">3423 </span>  ]
-<span id="L3424" class="LineNr">3424 </span>  run [
-<span id="L3425" class="LineNr">3425 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3426" class="LineNr">3426 </span>  ]
-<span id="L3427" class="LineNr">3427 </span>  screen-should-contain [
-<span id="L3428" class="LineNr">3428 </span>   <span class="Constant"> .          .</span>
+<span id="L3375" class="LineNr">3375 </span>  screen-should-contain [
+<span id="L3376" class="LineNr">3376 </span>   <span class="Constant"> .          .</span>
+<span id="L3377" class="LineNr">3377 </span>   <span class="Constant"> .g         .</span>
+<span id="L3378" class="LineNr">3378 </span>   <span class="Constant"> .h         .</span>
+<span id="L3379" class="LineNr">3379 </span>   <span class="Constant"> .i         .</span>
+<span id="L3380" class="LineNr">3380 </span>  ]
+<span id="L3381" class="LineNr">3381 </span>  <span class="Comment"># now move up one line</span>
+<span id="L3382" class="LineNr">3382 </span>  assume-console [
+<span id="L3383" class="LineNr">3383 </span>    press up-arrow
+<span id="L3384" class="LineNr">3384 </span>  ]
+<span id="L3385" class="LineNr">3385 </span>  run [
+<span id="L3386" class="LineNr">3386 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3387" class="LineNr">3387 </span>  ]
+<span id="L3388" class="LineNr">3388 </span>  <span class="Comment"># screen shows partial wrapped line</span>
+<span id="L3389" class="LineNr">3389 </span>  screen-should-contain [
+<span id="L3390" class="LineNr">3390 </span>   <span class="Constant"> .          .</span>
+<span id="L3391" class="LineNr">3391 </span>   <span class="Constant"> .f         .</span>
+<span id="L3392" class="LineNr">3392 </span>   <span class="Constant"> .g         .</span>
+<span id="L3393" class="LineNr">3393 </span>   <span class="Constant"> .h         .</span>
+<span id="L3394" class="LineNr">3394 </span>  ]
+<span id="L3395" class="LineNr">3395 </span>]
+<span id="L3396" class="LineNr">3396 </span>
+<span id="L3397" class="LineNr">3397 </span><span class="Comment"># check empty lines</span>
+<span id="L3398" class="LineNr">3398 </span><span class="muScenario">scenario</span> editor-scrolls-up-past-wrapped-line-using-arrow-keys-4 [
+<span id="L3399" class="LineNr">3399 </span>  <span class="Constant">local-scope</span>
+<span id="L3400" class="LineNr">3400 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3401" class="LineNr">3401 </span>  <span class="Comment"># initialize editor with some lines around an empty line</span>
+<span id="L3402" class="LineNr">3402 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3403" class="LineNr">3403 </span><span class="Constant">b</span>
+<span id="L3404" class="LineNr">3404 </span>
+<span id="L3405" class="LineNr">3405 </span>c
+<span id="L3406" class="LineNr">3406 </span>d
+<span id="L3407" class="LineNr">3407 </span>e]
+<span id="L3408" class="LineNr">3408 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">6/right</span>
+<span id="L3409" class="LineNr">3409 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3410" class="LineNr">3410 </span>  assume-console [
+<span id="L3411" class="LineNr">3411 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3412" class="LineNr">3412 </span>  ]
+<span id="L3413" class="LineNr">3413 </span>  run [
+<span id="L3414" class="LineNr">3414 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3415" class="LineNr">3415 </span>  ]
+<span id="L3416" class="LineNr">3416 </span>  screen-should-contain [
+<span id="L3417" class="LineNr">3417 </span>   <span class="Constant"> .          .</span>
+<span id="L3418" class="LineNr">3418 </span>   <span class="Constant"> .          .</span>
+<span id="L3419" class="LineNr">3419 </span>   <span class="Constant"> .c         .</span>
+<span id="L3420" class="LineNr">3420 </span>   <span class="Constant"> .d         .</span>
+<span id="L3421" class="LineNr">3421 </span>  ]
+<span id="L3422" class="LineNr">3422 </span>  assume-console [
+<span id="L3423" class="LineNr">3423 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3424" class="LineNr">3424 </span>  ]
+<span id="L3425" class="LineNr">3425 </span>  run [
+<span id="L3426" class="LineNr">3426 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3427" class="LineNr">3427 </span>  ]
+<span id="L3428" class="LineNr">3428 </span>  screen-should-contain [
 <span id="L3429" class="LineNr">3429 </span>   <span class="Constant"> .          .</span>
-<span id="L3430" class="LineNr">3430 </span>   <span class="Constant"> .c         .</span>
-<span id="L3431" class="LineNr">3431 </span>   <span class="Constant"> .d         .</span>
-<span id="L3432" class="LineNr">3432 </span>  ]
-<span id="L3433" class="LineNr">3433 </span>]
-<span id="L3434" class="LineNr">3434 </span>
-<span id="L3435" class="LineNr">3435 </span><span class="muScenario">scenario</span> editor-scrolls-up-on-left-arrow [
-<span id="L3436" class="LineNr">3436 </span>  <span class="Constant">local-scope</span>
-<span id="L3437" class="LineNr">3437 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3438" class="LineNr">3438 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
-<span id="L3439" class="LineNr">3439 </span>  <span class="Comment"># editor contains &gt;3 lines</span>
-<span id="L3440" class="LineNr">3440 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3441" class="LineNr">3441 </span><span class="Constant">b</span>
-<span id="L3442" class="LineNr">3442 </span><span class="Constant">c</span>
-<span id="L3443" class="LineNr">3443 </span><span class="Constant">d</span>
-<span id="L3444" class="LineNr">3444 </span><span class="Constant">e]</span>
-<span id="L3445" class="LineNr">3445 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L3446" class="LineNr">3446 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3447" class="LineNr">3447 </span>  <span class="Comment"># position cursor at top of second page</span>
-<span id="L3448" class="LineNr">3448 </span>  assume-console [
-<span id="L3449" class="LineNr">3449 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3450" class="LineNr">3450 </span>  ]
-<span id="L3451" class="LineNr">3451 </span>  run [
-<span id="L3452" class="LineNr">3452 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3453" class="LineNr">3453 </span>  ]
-<span id="L3454" class="LineNr">3454 </span>  screen-should-contain [
-<span id="L3455" class="LineNr">3455 </span>   <span class="Constant"> .     .</span>
-<span id="L3456" class="LineNr">3456 </span>   <span class="Constant"> .c    .</span>
-<span id="L3457" class="LineNr">3457 </span>   <span class="Constant"> .d    .</span>
-<span id="L3458" class="LineNr">3458 </span>   <span class="Constant"> .e    .</span>
-<span id="L3459" class="LineNr">3459 </span>  ]
-<span id="L3460" class="LineNr">3460 </span>  <span class="Comment"># now try to move left</span>
+<span id="L3430" class="LineNr">3430 </span>   <span class="Constant"> .d         .</span>
+<span id="L3431" class="LineNr">3431 </span>   <span class="Constant"> .e         .</span>
+<span id="L3432" class="LineNr">3432 </span>   <span class="Constant"> .╌╌╌╌╌╌    .</span>
+<span id="L3433" class="LineNr">3433 </span>  ]
+<span id="L3434" class="LineNr">3434 </span>  assume-console [
+<span id="L3435" class="LineNr">3435 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L3436" class="LineNr">3436 </span>  ]
+<span id="L3437" class="LineNr">3437 </span>  run [
+<span id="L3438" class="LineNr">3438 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3439" class="LineNr">3439 </span>  ]
+<span id="L3440" class="LineNr">3440 </span>  screen-should-contain [
+<span id="L3441" class="LineNr">3441 </span>   <span class="Constant"> .          .</span>
+<span id="L3442" class="LineNr">3442 </span>   <span class="Constant"> .          .</span>
+<span id="L3443" class="LineNr">3443 </span>   <span class="Constant"> .c         .</span>
+<span id="L3444" class="LineNr">3444 </span>   <span class="Constant"> .d         .</span>
+<span id="L3445" class="LineNr">3445 </span>  ]
+<span id="L3446" class="LineNr">3446 </span>]
+<span id="L3447" class="LineNr">3447 </span>
+<span id="L3448" class="LineNr">3448 </span><span class="muScenario">scenario</span> editor-scrolls-up-on-left-arrow [
+<span id="L3449" class="LineNr">3449 </span>  <span class="Constant">local-scope</span>
+<span id="L3450" class="LineNr">3450 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3451" class="LineNr">3451 </span>  assume-screen <span class="Constant">5/width</span>, <span class="Constant">4/height</span>
+<span id="L3452" class="LineNr">3452 </span>  <span class="Comment"># editor contains &gt;3 lines</span>
+<span id="L3453" class="LineNr">3453 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3454" class="LineNr">3454 </span><span class="Constant">b</span>
+<span id="L3455" class="LineNr">3455 </span><span class="Constant">c</span>
+<span id="L3456" class="LineNr">3456 </span><span class="Constant">d</span>
+<span id="L3457" class="LineNr">3457 </span><span class="Constant">e]</span>
+<span id="L3458" class="LineNr">3458 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L3459" class="LineNr">3459 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
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 <span id="L3461" class="LineNr">3461 </span>  assume-console [
-<span id="L3462" class="LineNr">3462 </span>    press left-arrow
+<span id="L3462" class="LineNr">3462 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L3463" class="LineNr">3463 </span>  ]
 <span id="L3464" class="LineNr">3464 </span>  run [
 <span id="L3465" class="LineNr">3465 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3466" class="LineNr">3466 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L3467" class="LineNr">3467 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
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-<span id="L3472" class="LineNr">3472 </span>   <span class="Constant"> .b    .</span>
-<span id="L3473" class="LineNr">3473 </span>   <span class="Constant"> .c    .</span>
-<span id="L3474" class="LineNr">3474 </span>   <span class="Constant"> .d    .</span>
-<span id="L3475" class="LineNr">3475 </span>  ]
-<span id="L3476" class="LineNr">3476 </span>  memory-should-contain [
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-<span id="L3478" class="LineNr">3478 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
-<span id="L3479" class="LineNr">3479 </span>  ]
-<span id="L3480" class="LineNr">3480 </span>]
-<span id="L3481" class="LineNr">3481 </span>
-<span id="L3482" class="LineNr">3482 </span><span class="muScenario">scenario</span> editor-can-scroll-up-to-start-of-file [
-<span id="L3483" class="LineNr">3483 </span>  <span class="Constant">local-scope</span>
-<span id="L3484" class="LineNr">3484 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3485" class="LineNr">3485 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3486" class="LineNr">3486 </span>  <span class="Comment"># initialize editor with &gt;3 lines</span>
-<span id="L3487" class="LineNr">3487 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3488" class="LineNr">3488 </span><span class="Constant">b</span>
-<span id="L3489" class="LineNr">3489 </span><span class="Constant">c</span>
-<span id="L3490" class="LineNr">3490 </span><span class="Constant">d]</span>
-<span id="L3491" class="LineNr">3491 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3492" class="LineNr">3492 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3493" class="LineNr">3493 </span>  screen-should-contain [
-<span id="L3494" class="LineNr">3494 </span>   <span class="Constant"> .          .</span>
-<span id="L3495" class="LineNr">3495 </span>   <span class="Constant"> .a         .</span>
-<span id="L3496" class="LineNr">3496 </span>   <span class="Constant"> .b         .</span>
-<span id="L3497" class="LineNr">3497 </span>   <span class="Constant"> .c         .</span>
-<span id="L3498" class="LineNr">3498 </span>  ]
-<span id="L3499" class="LineNr">3499 </span>  <span class="Comment"># position cursor at top of second page, then try to move up to start of</span>
-<span id="L3500" class="LineNr">3500 </span>  <span class="Comment"># text</span>
-<span id="L3501" class="LineNr">3501 </span>  assume-console [
-<span id="L3502" class="LineNr">3502 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3503" class="LineNr">3503 </span>    press up-arrow
-<span id="L3504" class="LineNr">3504 </span>    press up-arrow
-<span id="L3505" class="LineNr">3505 </span>  ]
-<span id="L3506" class="LineNr">3506 </span>  run [
-<span id="L3507" class="LineNr">3507 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3508" class="LineNr">3508 </span>  ]
-<span id="L3509" class="LineNr">3509 </span>  <span class="Comment"># screen slides by one line</span>
-<span id="L3510" class="LineNr">3510 </span>  screen-should-contain [
-<span id="L3511" class="LineNr">3511 </span>   <span class="Constant"> .          .</span>
-<span id="L3512" class="LineNr">3512 </span>   <span class="Constant"> .a         .</span>
-<span id="L3513" class="LineNr">3513 </span>   <span class="Constant"> .b         .</span>
-<span id="L3514" class="LineNr">3514 </span>   <span class="Constant"> .c         .</span>
-<span id="L3515" class="LineNr">3515 </span>  ]
-<span id="L3516" class="LineNr">3516 </span>  <span class="Comment"># try to move up again</span>
-<span id="L3517" class="LineNr">3517 </span>  assume-console [
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-<span id="L3519" class="LineNr">3519 </span>  ]
-<span id="L3520" class="LineNr">3520 </span>  run [
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-<span id="L3522" class="LineNr">3522 </span>  ]
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-<span id="L3524" class="LineNr">3524 </span>  screen-should-contain [
-<span id="L3525" class="LineNr">3525 </span>   <span class="Constant"> .          .</span>
-<span id="L3526" class="LineNr">3526 </span>   <span class="Constant"> .a         .</span>
-<span id="L3527" class="LineNr">3527 </span>   <span class="Constant"> .b         .</span>
-<span id="L3528" class="LineNr">3528 </span>   <span class="Constant"> .c         .</span>
-<span id="L3529" class="LineNr">3529 </span>  ]
-<span id="L3530" class="LineNr">3530 </span>]
-<span id="L3531" class="LineNr">3531 </span>
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-<span id="L3533" class="LineNr">3533 </span>
-<span id="L3534" class="LineNr">3534 </span><span class="muScenario">scenario</span> editor-can-scroll [
-<span id="L3535" class="LineNr">3535 </span>  <span class="Constant">local-scope</span>
-<span id="L3536" class="LineNr">3536 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3537" class="LineNr">3537 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3538" class="LineNr">3538 </span><span class="Constant">b</span>
-<span id="L3539" class="LineNr">3539 </span><span class="Constant">c</span>
-<span id="L3540" class="LineNr">3540 </span><span class="Constant">d]</span>
-<span id="L3541" class="LineNr">3541 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3542" class="LineNr">3542 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3543" class="LineNr">3543 </span>  screen-should-contain [
-<span id="L3544" class="LineNr">3544 </span>   <span class="Constant"> .          .</span>
-<span id="L3545" class="LineNr">3545 </span>   <span class="Constant"> .a         .</span>
-<span id="L3546" class="LineNr">3546 </span>   <span class="Constant"> .b         .</span>
-<span id="L3547" class="LineNr">3547 </span>   <span class="Constant"> .c         .</span>
-<span id="L3548" class="LineNr">3548 </span>  ]
-<span id="L3549" class="LineNr">3549 </span>  <span class="Comment"># scroll down</span>
-<span id="L3550" class="LineNr">3550 </span>  assume-console [
-<span id="L3551" class="LineNr">3551 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3552" class="LineNr">3552 </span>  ]
-<span id="L3553" class="LineNr">3553 </span>  run [
-<span id="L3554" class="LineNr">3554 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3555" class="LineNr">3555 </span>  ]
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-<span id="L3557" class="LineNr">3557 </span>  screen-should-contain [
-<span id="L3558" class="LineNr">3558 </span>   <span class="Constant"> .          .</span>
-<span id="L3559" class="LineNr">3559 </span>   <span class="Constant"> .c         .</span>
-<span id="L3560" class="LineNr">3560 </span>   <span class="Constant"> .d         .</span>
-<span id="L3561" class="LineNr">3561 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L3562" class="LineNr">3562 </span>  ]
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-<span id="L3564" class="LineNr">3564 </span>
-<span id="L3565" class="LineNr">3565 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
-<span id="L3566" class="LineNr">3566 </span>  <span class="Delimiter">{</span>
-<span id="L3567" class="LineNr">3567 </span>    page-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">6/ctrl-f</span>
-<span id="L3568" class="LineNr">3568 </span>    <span class="muControl">break-unless</span> page-down?
-<span id="L3569" class="LineNr">3569 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3570" class="LineNr">3570 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L3571" class="LineNr">3571 </span>    <a href='003-shortcuts.mu.html#L3597'>page-down</a> editor
-<span id="L3572" class="LineNr">3572 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
-<span id="L3573" class="LineNr">3573 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L3574" class="LineNr">3574 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3575" class="LineNr">3575 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
-<span id="L3576" class="LineNr">3576 </span>   <span class="muControl"> return</span> movement?/go-render
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-<span id="L3578" class="LineNr">3578 </span>]
-<span id="L3579" class="LineNr">3579 </span>
-<span id="L3580" class="LineNr">3580 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L199'>&lt;handle-special-key&gt;</a></span> [
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-<span id="L3583" class="LineNr">3583 </span>    <span class="muControl">break-unless</span> page-down?
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-<span id="L3585" class="LineNr">3585 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L3586" class="LineNr">3586 </span>    <a href='003-shortcuts.mu.html#L3597'>page-down</a> editor
-<span id="L3587" class="LineNr">3587 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
-<span id="L3588" class="LineNr">3588 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L3589" class="LineNr">3589 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3590" class="LineNr">3590 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
-<span id="L3591" class="LineNr">3591 </span>   <span class="muControl"> return</span> movement?/go-render
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-<span id="L3594" class="LineNr">3594 </span>
-<span id="L3595" class="LineNr">3595 </span><span class="Comment"># page-down skips entire wrapped lines, so it can't scroll past lines</span>
-<span id="L3596" class="LineNr">3596 </span><span class="Comment"># taking up the entire screen</span>
-<span id="L3597" class="LineNr">3597 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3597'>page-down</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
-<span id="L3598" class="LineNr">3598 </span>  <span class="Constant">local-scope</span>
-<span id="L3599" class="LineNr">3599 </span>  <span class="Constant">load-inputs</span>
-<span id="L3600" class="LineNr">3600 </span>  <span class="Comment"># if editor contents don't overflow screen, do nothing</span>
-<span id="L3601" class="LineNr">3601 </span>  bottom-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">bottom-of-screen:offset</span>
-<span id="L3602" class="LineNr">3602 </span>  <span class="muControl">return-unless</span> bottom-of-screen
-<span id="L3603" class="LineNr">3603 </span>  <span class="Comment"># if not, position cursor at final character</span>
-<span id="L3604" class="LineNr">3604 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L3605" class="LineNr">3605 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> bottom-of-screen
-<span id="L3606" class="LineNr">3606 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L3607" class="LineNr">3607 </span>  <span class="Comment"># keep one line in common with previous page</span>
-<span id="L3608" class="LineNr">3608 </span>  <span class="Delimiter">{</span>
-<span id="L3609" class="LineNr">3609 </span>    <a href='../065duplex_list.mu.html#L572'>last</a>:char <span class="Special">&lt;-</span> get *before-cursor, <span class="Constant">value:offset</span>
-<span id="L3610" class="LineNr">3610 </span>    newline?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L572'>last</a>, <span class="Constant">10/newline</span>
-<span id="L3611" class="LineNr">3611 </span>    <span class="muControl">break-unless</span> newline?:bool
-<span id="L3612" class="LineNr">3612 </span>    before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
-<span id="L3613" class="LineNr">3613 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L3614" class="LineNr">3614 </span>  <span class="Delimiter">}</span>
-<span id="L3615" class="LineNr">3615 </span>  <span class="Comment"># move cursor and top-of-screen to start of that line</span>
-<span id="L3616" class="LineNr">3616 </span>  <a href='003-shortcuts.mu.html#L3622'>move-to-start-of-line</a> editor
-<span id="L3617" class="LineNr">3617 </span>  before-cursor <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L3618" class="LineNr">3618 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, before-cursor
-<span id="L3619" class="LineNr">3619 </span>]
-<span id="L3620" class="LineNr">3620 </span>
-<span id="L3621" class="LineNr">3621 </span><span class="Comment"># jump to previous newline</span>
-<span id="L3622" class="LineNr">3622 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3622'>move-to-start-of-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
-<span id="L3623" class="LineNr">3623 </span>  <span class="Constant">local-scope</span>
-<span id="L3624" class="LineNr">3624 </span>  <span class="Constant">load-inputs</span>
-<span id="L3625" class="LineNr">3625 </span>  <span class="Comment"># update cursor column</span>
-<span id="L3626" class="LineNr">3626 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
-<span id="L3627" class="LineNr">3627 </span>  cursor-column:num <span class="Special">&lt;-</span> copy left
-<span id="L3628" class="LineNr">3628 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L3629" class="LineNr">3629 </span>  <span class="Comment"># update before-cursor</span>
-<span id="L3630" class="LineNr">3630 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L3631" class="LineNr">3631 </span>  init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L3632" class="LineNr">3632 </span>  <span class="Comment"># while not at start of line, move</span>
-<span id="L3633" class="LineNr">3633 </span>  <span class="Delimiter">{</span>
-<span id="L3634" class="LineNr">3634 </span>    at-start-of-text?:bool <span class="Special">&lt;-</span> equal before-cursor, init
-<span id="L3635" class="LineNr">3635 </span>    <span class="muControl">break-if</span> at-start-of-text?
-<span id="L3636" class="LineNr">3636 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a>:char <span class="Special">&lt;-</span> get *before-cursor, <span class="Constant">value:offset</span>
-<span id="L3637" class="LineNr">3637 </span>    at-start-of-line?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L32'>prev</a>, <span class="Constant">10/newline</span>
-<span id="L3638" class="LineNr">3638 </span>    <span class="muControl">break-if</span> at-start-of-line?
-<span id="L3639" class="LineNr">3639 </span>    before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> before-cursor
-<span id="L3640" class="LineNr">3640 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L3641" class="LineNr">3641 </span>    assert before-cursor, <span class="Constant">[move-to-start-of-line tried to move before start of text]</span>
-<span id="L3642" class="LineNr">3642 </span>   <span class="muControl"> loop</span>
-<span id="L3643" class="LineNr">3643 </span>  <span class="Delimiter">}</span>
-<span id="L3644" class="LineNr">3644 </span>]
-<span id="L3645" class="LineNr">3645 </span>
-<span id="L3646" class="LineNr">3646 </span><span class="muScenario">scenario</span> editor-does-not-scroll-past-end [
-<span id="L3647" class="LineNr">3647 </span>  <span class="Constant">local-scope</span>
-<span id="L3648" class="LineNr">3648 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3649" class="LineNr">3649 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3650" class="LineNr">3650 </span><span class="Constant">b]</span>
-<span id="L3651" class="LineNr">3651 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3652" class="LineNr">3652 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3653" class="LineNr">3653 </span>  screen-should-contain [
-<span id="L3654" class="LineNr">3654 </span>   <span class="Constant"> .          .</span>
-<span id="L3655" class="LineNr">3655 </span>   <span class="Constant"> .a         .</span>
-<span id="L3656" class="LineNr">3656 </span>   <span class="Constant"> .b         .</span>
-<span id="L3657" class="LineNr">3657 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L3658" class="LineNr">3658 </span>  ]
-<span id="L3659" class="LineNr">3659 </span>  <span class="Comment"># scroll down</span>
-<span id="L3660" class="LineNr">3660 </span>  assume-console [
-<span id="L3661" class="LineNr">3661 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3662" class="LineNr">3662 </span>  ]
-<span id="L3663" class="LineNr">3663 </span>  run [
-<span id="L3664" class="LineNr">3664 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3665" class="LineNr">3665 </span>  ]
-<span id="L3666" class="LineNr">3666 </span>  <span class="Comment"># screen remains unmodified</span>
-<span id="L3667" class="LineNr">3667 </span>  screen-should-contain [
-<span id="L3668" class="LineNr">3668 </span>   <span class="Constant"> .          .</span>
-<span id="L3669" class="LineNr">3669 </span>   <span class="Constant"> .a         .</span>
-<span id="L3670" class="LineNr">3670 </span>   <span class="Constant"> .b         .</span>
-<span id="L3671" class="LineNr">3671 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L3672" class="LineNr">3672 </span>  ]
-<span id="L3673" class="LineNr">3673 </span>]
-<span id="L3674" class="LineNr">3674 </span>
-<span id="L3675" class="LineNr">3675 </span><span class="muScenario">scenario</span> editor-starts-next-page-at-start-of-wrapped-line [
-<span id="L3676" class="LineNr">3676 </span>  <span class="Constant">local-scope</span>
-<span id="L3677" class="LineNr">3677 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
-<span id="L3678" class="LineNr">3678 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3679" class="LineNr">3679 </span>  <span class="Comment"># editor contains a long last line</span>
-<span id="L3680" class="LineNr">3680 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3681" class="LineNr">3681 </span><span class="Constant">b</span>
-<span id="L3682" class="LineNr">3682 </span><span class="Constant">cdefgh]</span>
-<span id="L3683" class="LineNr">3683 </span>  <span class="Comment"># editor screen triggers wrap of last line</span>
-<span id="L3684" class="LineNr">3684 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L3685" class="LineNr">3685 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3686" class="LineNr">3686 </span>  <span class="Comment"># some part of last line is not displayed</span>
-<span id="L3687" class="LineNr">3687 </span>  screen-should-contain [
-<span id="L3688" class="LineNr">3688 </span>   <span class="Constant"> .          .</span>
-<span id="L3689" class="LineNr">3689 </span>   <span class="Constant"> .a         .</span>
-<span id="L3690" class="LineNr">3690 </span>   <span class="Constant"> .b         .</span>
-<span id="L3691" class="LineNr">3691 </span>   <span class="Constant"> .cde↩      .</span>
-<span id="L3692" class="LineNr">3692 </span>  ]
-<span id="L3693" class="LineNr">3693 </span>  <span class="Comment"># scroll down</span>
-<span id="L3694" class="LineNr">3694 </span>  assume-console [
-<span id="L3695" class="LineNr">3695 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3696" class="LineNr">3696 </span>  ]
-<span id="L3697" class="LineNr">3697 </span>  run [
-<span id="L3698" class="LineNr">3698 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3699" class="LineNr">3699 </span>  ]
-<span id="L3700" class="LineNr">3700 </span>  <span class="Comment"># screen shows entire wrapped line</span>
-<span id="L3701" class="LineNr">3701 </span>  screen-should-contain [
-<span id="L3702" class="LineNr">3702 </span>   <span class="Constant"> .          .</span>
-<span id="L3703" class="LineNr">3703 </span>   <span class="Constant"> .cde↩      .</span>
-<span id="L3704" class="LineNr">3704 </span>   <span class="Constant"> .fgh       .</span>
-<span id="L3705" class="LineNr">3705 </span>   <span class="Constant"> .╌╌╌╌      .</span>
-<span id="L3706" class="LineNr">3706 </span>  ]
-<span id="L3707" class="LineNr">3707 </span>]
-<span id="L3708" class="LineNr">3708 </span>
-<span id="L3709" class="LineNr">3709 </span><span class="muScenario">scenario</span> editor-starts-next-page-at-start-of-wrapped-line-2 [
-<span id="L3710" class="LineNr">3710 </span>  <span class="Constant">local-scope</span>
-<span id="L3711" class="LineNr">3711 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
-<span id="L3712" class="LineNr">3712 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3713" class="LineNr">3713 </span>  <span class="Comment"># editor contains a very long line that occupies last two lines of screen</span>
-<span id="L3714" class="LineNr">3714 </span>  <span class="Comment"># and still has something left over</span>
-<span id="L3715" class="LineNr">3715 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3716" class="LineNr">3716 </span><span class="Constant">bcdefgh]</span>
-<span id="L3717" class="LineNr">3717 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L3718" class="LineNr">3718 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3719" class="LineNr">3719 </span>  <span class="Comment"># some part of last line is not displayed</span>
-<span id="L3720" class="LineNr">3720 </span>  screen-should-contain [
-<span id="L3721" class="LineNr">3721 </span>   <span class="Constant"> .          .</span>
-<span id="L3722" class="LineNr">3722 </span>   <span class="Constant"> .a         .</span>
-<span id="L3723" class="LineNr">3723 </span>   <span class="Constant"> .bcd↩      .</span>
-<span id="L3724" class="LineNr">3724 </span>   <span class="Constant"> .efg↩      .</span>
-<span id="L3725" class="LineNr">3725 </span>  ]
-<span id="L3726" class="LineNr">3726 </span>  <span class="Comment"># scroll down</span>
-<span id="L3727" class="LineNr">3727 </span>  assume-console [
-<span id="L3728" class="LineNr">3728 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3729" class="LineNr">3729 </span>  ]
-<span id="L3730" class="LineNr">3730 </span>  run [
-<span id="L3731" class="LineNr">3731 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3732" class="LineNr">3732 </span>  ]
-<span id="L3733" class="LineNr">3733 </span>  <span class="Comment"># screen shows entire wrapped line</span>
-<span id="L3734" class="LineNr">3734 </span>  screen-should-contain [
-<span id="L3735" class="LineNr">3735 </span>   <span class="Constant"> .          .</span>
+<span id="L3466" class="LineNr">3466 </span>  ]
+<span id="L3467" class="LineNr">3467 </span>  screen-should-contain [
+<span id="L3468" class="LineNr">3468 </span>   <span class="Constant"> .     .</span>
+<span id="L3469" class="LineNr">3469 </span>   <span class="Constant"> .c    .</span>
+<span id="L3470" class="LineNr">3470 </span>   <span class="Constant"> .d    .</span>
+<span id="L3471" class="LineNr">3471 </span>   <span class="Constant"> .e    .</span>
+<span id="L3472" class="LineNr">3472 </span>  ]
+<span id="L3473" class="LineNr">3473 </span>  <span class="Comment"># now try to move left</span>
+<span id="L3474" class="LineNr">3474 </span>  assume-console [
+<span id="L3475" class="LineNr">3475 </span>    press left-arrow
+<span id="L3476" class="LineNr">3476 </span>  ]
+<span id="L3477" class="LineNr">3477 </span>  run [
+<span id="L3478" class="LineNr">3478 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3479" class="LineNr">3479 </span>    3:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L3480" class="LineNr">3480 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L3481" class="LineNr">3481 </span>  ]
+<span id="L3482" class="LineNr">3482 </span>  <span class="Comment"># screen scrolls</span>
+<span id="L3483" class="LineNr">3483 </span>  screen-should-contain [
+<span id="L3484" class="LineNr">3484 </span>   <span class="Constant"> .     .</span>
+<span id="L3485" class="LineNr">3485 </span>   <span class="Constant"> .b    .</span>
+<span id="L3486" class="LineNr">3486 </span>   <span class="Constant"> .c    .</span>
+<span id="L3487" class="LineNr">3487 </span>   <span class="Constant"> .d    .</span>
+<span id="L3488" class="LineNr">3488 </span>  ]
+<span id="L3489" class="LineNr">3489 </span>  memory-should-contain [
+<span id="L3490" class="LineNr">3490 </span>   <span class="Constant"> 3</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
+<span id="L3491" class="LineNr">3491 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
+<span id="L3492" class="LineNr">3492 </span>  ]
+<span id="L3493" class="LineNr">3493 </span>]
+<span id="L3494" class="LineNr">3494 </span>
+<span id="L3495" class="LineNr">3495 </span><span class="muScenario">scenario</span> editor-can-scroll-up-to-start-of-file [
+<span id="L3496" class="LineNr">3496 </span>  <span class="Constant">local-scope</span>
+<span id="L3497" class="LineNr">3497 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3498" class="LineNr">3498 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3499" class="LineNr">3499 </span>  <span class="Comment"># initialize editor with &gt;3 lines</span>
+<span id="L3500" class="LineNr">3500 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3501" class="LineNr">3501 </span><span class="Constant">b</span>
+<span id="L3502" class="LineNr">3502 </span><span class="Constant">c</span>
+<span id="L3503" class="LineNr">3503 </span><span class="Constant">d]</span>
+<span id="L3504" class="LineNr">3504 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3505" class="LineNr">3505 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3506" class="LineNr">3506 </span>  screen-should-contain [
+<span id="L3507" class="LineNr">3507 </span>   <span class="Constant"> .          .</span>
+<span id="L3508" class="LineNr">3508 </span>   <span class="Constant"> .a         .</span>
+<span id="L3509" class="LineNr">3509 </span>   <span class="Constant"> .b         .</span>
+<span id="L3510" class="LineNr">3510 </span>   <span class="Constant"> .c         .</span>
+<span id="L3511" class="LineNr">3511 </span>  ]
+<span id="L3512" class="LineNr">3512 </span>  <span class="Comment"># position cursor at top of second page, then try to move up to start of</span>
+<span id="L3513" class="LineNr">3513 </span>  <span class="Comment"># text</span>
+<span id="L3514" class="LineNr">3514 </span>  assume-console [
+<span id="L3515" class="LineNr">3515 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3516" class="LineNr">3516 </span>    press up-arrow
+<span id="L3517" class="LineNr">3517 </span>    press up-arrow
+<span id="L3518" class="LineNr">3518 </span>  ]
+<span id="L3519" class="LineNr">3519 </span>  run [
+<span id="L3520" class="LineNr">3520 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3521" class="LineNr">3521 </span>  ]
+<span id="L3522" class="LineNr">3522 </span>  <span class="Comment"># screen slides by one line</span>
+<span id="L3523" class="LineNr">3523 </span>  screen-should-contain [
+<span id="L3524" class="LineNr">3524 </span>   <span class="Constant"> .          .</span>
+<span id="L3525" class="LineNr">3525 </span>   <span class="Constant"> .a         .</span>
+<span id="L3526" class="LineNr">3526 </span>   <span class="Constant"> .b         .</span>
+<span id="L3527" class="LineNr">3527 </span>   <span class="Constant"> .c         .</span>
+<span id="L3528" class="LineNr">3528 </span>  ]
+<span id="L3529" class="LineNr">3529 </span>  <span class="Comment"># try to move up again</span>
+<span id="L3530" class="LineNr">3530 </span>  assume-console [
+<span id="L3531" class="LineNr">3531 </span>    press up-arrow
+<span id="L3532" class="LineNr">3532 </span>  ]
+<span id="L3533" class="LineNr">3533 </span>  run [
+<span id="L3534" class="LineNr">3534 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3535" class="LineNr">3535 </span>  ]
+<span id="L3536" class="LineNr">3536 </span>  <span class="Comment"># screen remains unchanged</span>
+<span id="L3537" class="LineNr">3537 </span>  screen-should-contain [
+<span id="L3538" class="LineNr">3538 </span>   <span class="Constant"> .          .</span>
+<span id="L3539" class="LineNr">3539 </span>   <span class="Constant"> .a         .</span>
+<span id="L3540" class="LineNr">3540 </span>   <span class="Constant"> .b         .</span>
+<span id="L3541" class="LineNr">3541 </span>   <span class="Constant"> .c         .</span>
+<span id="L3542" class="LineNr">3542 </span>  ]
+<span id="L3543" class="LineNr">3543 </span>]
+<span id="L3544" class="LineNr">3544 </span>
+<span id="L3545" class="LineNr">3545 </span><span class="Comment"># ctrl-f/page-down - render next page if it exists</span>
+<span id="L3546" class="LineNr">3546 </span>
+<span id="L3547" class="LineNr">3547 </span><span class="muScenario">scenario</span> editor-can-scroll [
+<span id="L3548" class="LineNr">3548 </span>  <span class="Constant">local-scope</span>
+<span id="L3549" class="LineNr">3549 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3550" class="LineNr">3550 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3551" class="LineNr">3551 </span><span class="Constant">b</span>
+<span id="L3552" class="LineNr">3552 </span><span class="Constant">c</span>
+<span id="L3553" class="LineNr">3553 </span><span class="Constant">d]</span>
+<span id="L3554" class="LineNr">3554 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3555" class="LineNr">3555 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3556" class="LineNr">3556 </span>  screen-should-contain [
+<span id="L3557" class="LineNr">3557 </span>   <span class="Constant"> .          .</span>
+<span id="L3558" class="LineNr">3558 </span>   <span class="Constant"> .a         .</span>
+<span id="L3559" class="LineNr">3559 </span>   <span class="Constant"> .b         .</span>
+<span id="L3560" class="LineNr">3560 </span>   <span class="Constant"> .c         .</span>
+<span id="L3561" class="LineNr">3561 </span>  ]
+<span id="L3562" class="LineNr">3562 </span>  <span class="Comment"># scroll down</span>
+<span id="L3563" class="LineNr">3563 </span>  assume-console [
+<span id="L3564" class="LineNr">3564 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3565" class="LineNr">3565 </span>  ]
+<span id="L3566" class="LineNr">3566 </span>  run [
+<span id="L3567" class="LineNr">3567 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3568" class="LineNr">3568 </span>  ]
+<span id="L3569" class="LineNr">3569 </span>  <span class="Comment"># screen shows next page</span>
+<span id="L3570" class="LineNr">3570 </span>  screen-should-contain [
+<span id="L3571" class="LineNr">3571 </span>   <span class="Constant"> .          .</span>
+<span id="L3572" class="LineNr">3572 </span>   <span class="Constant"> .c         .</span>
+<span id="L3573" class="LineNr">3573 </span>   <span class="Constant"> .d         .</span>
+<span id="L3574" class="LineNr">3574 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3575" class="LineNr">3575 </span>  ]
+<span id="L3576" class="LineNr">3576 </span>]
+<span id="L3577" class="LineNr">3577 </span>
+<span id="L3578" class="LineNr">3578 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L3579" class="LineNr">3579 </span>  <span class="Delimiter">{</span>
+<span id="L3580" class="LineNr">3580 </span>    page-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">6/ctrl-f</span>
+<span id="L3581" class="LineNr">3581 </span>    <span class="muControl">break-unless</span> page-down?
+<span id="L3582" class="LineNr">3582 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3583" class="LineNr">3583 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L3584" class="LineNr">3584 </span>    <a href='003-shortcuts.mu.html#L3610'>page-down</a> editor
+<span id="L3585" class="LineNr">3585 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
+<span id="L3586" class="LineNr">3586 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L3587" class="LineNr">3587 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3588" class="LineNr">3588 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
+<span id="L3589" class="LineNr">3589 </span>   <span class="muControl"> return</span> movement?/go-render
+<span id="L3590" class="LineNr">3590 </span>  <span class="Delimiter">}</span>
+<span id="L3591" class="LineNr">3591 </span>]
+<span id="L3592" class="LineNr">3592 </span>
+<span id="L3593" class="LineNr">3593 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L199'>&lt;handle-special-key&gt;</a></span> [
+<span id="L3594" class="LineNr">3594 </span>  <span class="Delimiter">{</span>
+<span id="L3595" class="LineNr">3595 </span>    page-down?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65518/page-down</span>
+<span id="L3596" class="LineNr">3596 </span>    <span class="muControl">break-unless</span> page-down?
+<span id="L3597" class="LineNr">3597 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3598" class="LineNr">3598 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L3599" class="LineNr">3599 </span>    <a href='003-shortcuts.mu.html#L3610'>page-down</a> editor
+<span id="L3600" class="LineNr">3600 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
+<span id="L3601" class="LineNr">3601 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L3602" class="LineNr">3602 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3603" class="LineNr">3603 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
+<span id="L3604" class="LineNr">3604 </span>   <span class="muControl"> return</span> movement?/go-render
+<span id="L3605" class="LineNr">3605 </span>  <span class="Delimiter">}</span>
+<span id="L3606" class="LineNr">3606 </span>]
+<span id="L3607" class="LineNr">3607 </span>
+<span id="L3608" class="LineNr">3608 </span><span class="Comment"># page-down skips entire wrapped lines, so it can't scroll past lines</span>
+<span id="L3609" class="LineNr">3609 </span><span class="Comment"># taking up the entire screen</span>
+<span id="L3610" class="LineNr">3610 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3610'>page-down</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
+<span id="L3611" class="LineNr">3611 </span>  <span class="Constant">local-scope</span>
+<span id="L3612" class="LineNr">3612 </span>  <span class="Constant">load-inputs</span>
+<span id="L3613" class="LineNr">3613 </span>  <span class="Comment"># if editor contents don't overflow screen, do nothing</span>
+<span id="L3614" class="LineNr">3614 </span>  bottom-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">bottom-of-screen:offset</span>
+<span id="L3615" class="LineNr">3615 </span>  <span class="muControl">return-unless</span> bottom-of-screen
+<span id="L3616" class="LineNr">3616 </span>  <span class="Comment"># if not, position cursor at final character</span>
+<span id="L3617" class="LineNr">3617 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
+<span id="L3618" class="LineNr">3618 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> bottom-of-screen
+<span id="L3619" class="LineNr">3619 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
+<span id="L3620" class="LineNr">3620 </span>  <span class="Comment"># keep one line in common with previous page</span>
+<span id="L3621" class="LineNr">3621 </span>  <span class="Delimiter">{</span>
+<span id="L3622" class="LineNr">3622 </span>    <a href='../065duplex_list.mu.html#L629'>last</a>:char <span class="Special">&lt;-</span> get *before-cursor, <span class="Constant">value:offset</span>
+<span id="L3623" class="LineNr">3623 </span>    newline?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L629'>last</a>, <span class="Constant">10/newline</span>
+<span id="L3624" class="LineNr">3624 </span>    <span class="muControl">break-unless</span> newline?:bool
+<span id="L3625" class="LineNr">3625 </span>    before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
+<span id="L3626" class="LineNr">3626 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
+<span id="L3627" class="LineNr">3627 </span>  <span class="Delimiter">}</span>
+<span id="L3628" class="LineNr">3628 </span>  <span class="Comment"># move cursor and top-of-screen to start of that line</span>
+<span id="L3629" class="LineNr">3629 </span>  <a href='003-shortcuts.mu.html#L3635'>move-to-start-of-line</a> editor
+<span id="L3630" class="LineNr">3630 </span>  before-cursor <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
+<span id="L3631" class="LineNr">3631 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, before-cursor
+<span id="L3632" class="LineNr">3632 </span>]
+<span id="L3633" class="LineNr">3633 </span>
+<span id="L3634" class="LineNr">3634 </span><span class="Comment"># jump to previous newline</span>
+<span id="L3635" class="LineNr">3635 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3635'>move-to-start-of-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
+<span id="L3636" class="LineNr">3636 </span>  <span class="Constant">local-scope</span>
+<span id="L3637" class="LineNr">3637 </span>  <span class="Constant">load-inputs</span>
+<span id="L3638" class="LineNr">3638 </span>  <span class="Comment"># update cursor column</span>
+<span id="L3639" class="LineNr">3639 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
+<span id="L3640" class="LineNr">3640 </span>  cursor-column:num <span class="Special">&lt;-</span> copy left
+<span id="L3641" class="LineNr">3641 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
+<span id="L3642" class="LineNr">3642 </span>  <span class="Comment"># update before-cursor</span>
+<span id="L3643" class="LineNr">3643 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
+<span id="L3644" class="LineNr">3644 </span>  init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
+<span id="L3645" class="LineNr">3645 </span>  <span class="Comment"># while not at start of line, move</span>
+<span id="L3646" class="LineNr">3646 </span>  <span class="Delimiter">{</span>
+<span id="L3647" class="LineNr">3647 </span>    at-start-of-text?:bool <span class="Special">&lt;-</span> equal before-cursor, init
+<span id="L3648" class="LineNr">3648 </span>    <span class="muControl">break-if</span> at-start-of-text?
+<span id="L3649" class="LineNr">3649 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a>:char <span class="Special">&lt;-</span> get *before-cursor, <span class="Constant">value:offset</span>
+<span id="L3650" class="LineNr">3650 </span>    at-start-of-line?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L38'>prev</a>, <span class="Constant">10/newline</span>
+<span id="L3651" class="LineNr">3651 </span>    <span class="muControl">break-if</span> at-start-of-line?
+<span id="L3652" class="LineNr">3652 </span>    before-cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> before-cursor
+<span id="L3653" class="LineNr">3653 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
+<span id="L3654" class="LineNr">3654 </span>    assert before-cursor, <span class="Constant">[move-to-start-of-line tried to move before start of text]</span>
+<span id="L3655" class="LineNr">3655 </span>   <span class="muControl"> loop</span>
+<span id="L3656" class="LineNr">3656 </span>  <span class="Delimiter">}</span>
+<span id="L3657" class="LineNr">3657 </span>]
+<span id="L3658" class="LineNr">3658 </span>
+<span id="L3659" class="LineNr">3659 </span><span class="muScenario">scenario</span> editor-does-not-scroll-past-end [
+<span id="L3660" class="LineNr">3660 </span>  <span class="Constant">local-scope</span>
+<span id="L3661" class="LineNr">3661 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3662" class="LineNr">3662 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3663" class="LineNr">3663 </span><span class="Constant">b]</span>
+<span id="L3664" class="LineNr">3664 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3665" class="LineNr">3665 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3666" class="LineNr">3666 </span>  screen-should-contain [
+<span id="L3667" class="LineNr">3667 </span>   <span class="Constant"> .          .</span>
+<span id="L3668" class="LineNr">3668 </span>   <span class="Constant"> .a         .</span>
+<span id="L3669" class="LineNr">3669 </span>   <span class="Constant"> .b         .</span>
+<span id="L3670" class="LineNr">3670 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3671" class="LineNr">3671 </span>  ]
+<span id="L3672" class="LineNr">3672 </span>  <span class="Comment"># scroll down</span>
+<span id="L3673" class="LineNr">3673 </span>  assume-console [
+<span id="L3674" class="LineNr">3674 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3675" class="LineNr">3675 </span>  ]
+<span id="L3676" class="LineNr">3676 </span>  run [
+<span id="L3677" class="LineNr">3677 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3678" class="LineNr">3678 </span>  ]
+<span id="L3679" class="LineNr">3679 </span>  <span class="Comment"># screen remains unmodified</span>
+<span id="L3680" class="LineNr">3680 </span>  screen-should-contain [
+<span id="L3681" class="LineNr">3681 </span>   <span class="Constant"> .          .</span>
+<span id="L3682" class="LineNr">3682 </span>   <span class="Constant"> .a         .</span>
+<span id="L3683" class="LineNr">3683 </span>   <span class="Constant"> .b         .</span>
+<span id="L3684" class="LineNr">3684 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3685" class="LineNr">3685 </span>  ]
+<span id="L3686" class="LineNr">3686 </span>]
+<span id="L3687" class="LineNr">3687 </span>
+<span id="L3688" class="LineNr">3688 </span><span class="muScenario">scenario</span> editor-starts-next-page-at-start-of-wrapped-line [
+<span id="L3689" class="LineNr">3689 </span>  <span class="Constant">local-scope</span>
+<span id="L3690" class="LineNr">3690 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
+<span id="L3691" class="LineNr">3691 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3692" class="LineNr">3692 </span>  <span class="Comment"># editor contains a long last line</span>
+<span id="L3693" class="LineNr">3693 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3694" class="LineNr">3694 </span><span class="Constant">b</span>
+<span id="L3695" class="LineNr">3695 </span><span class="Constant">cdefgh]</span>
+<span id="L3696" class="LineNr">3696 </span>  <span class="Comment"># editor screen triggers wrap of last line</span>
+<span id="L3697" class="LineNr">3697 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L3698" class="LineNr">3698 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3699" class="LineNr">3699 </span>  <span class="Comment"># some part of last line is not displayed</span>
+<span id="L3700" class="LineNr">3700 </span>  screen-should-contain [
+<span id="L3701" class="LineNr">3701 </span>   <span class="Constant"> .          .</span>
+<span id="L3702" class="LineNr">3702 </span>   <span class="Constant"> .a         .</span>
+<span id="L3703" class="LineNr">3703 </span>   <span class="Constant"> .b         .</span>
+<span id="L3704" class="LineNr">3704 </span>   <span class="Constant"> .cde↩      .</span>
+<span id="L3705" class="LineNr">3705 </span>  ]
+<span id="L3706" class="LineNr">3706 </span>  <span class="Comment"># scroll down</span>
+<span id="L3707" class="LineNr">3707 </span>  assume-console [
+<span id="L3708" class="LineNr">3708 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3709" class="LineNr">3709 </span>  ]
+<span id="L3710" class="LineNr">3710 </span>  run [
+<span id="L3711" class="LineNr">3711 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3712" class="LineNr">3712 </span>  ]
+<span id="L3713" class="LineNr">3713 </span>  <span class="Comment"># screen shows entire wrapped line</span>
+<span id="L3714" class="LineNr">3714 </span>  screen-should-contain [
+<span id="L3715" class="LineNr">3715 </span>   <span class="Constant"> .          .</span>
+<span id="L3716" class="LineNr">3716 </span>   <span class="Constant"> .cde↩      .</span>
+<span id="L3717" class="LineNr">3717 </span>   <span class="Constant"> .fgh       .</span>
+<span id="L3718" class="LineNr">3718 </span>   <span class="Constant"> .╌╌╌╌      .</span>
+<span id="L3719" class="LineNr">3719 </span>  ]
+<span id="L3720" class="LineNr">3720 </span>]
+<span id="L3721" class="LineNr">3721 </span>
+<span id="L3722" class="LineNr">3722 </span><span class="muScenario">scenario</span> editor-starts-next-page-at-start-of-wrapped-line-2 [
+<span id="L3723" class="LineNr">3723 </span>  <span class="Constant">local-scope</span>
+<span id="L3724" class="LineNr">3724 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
+<span id="L3725" class="LineNr">3725 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3726" class="LineNr">3726 </span>  <span class="Comment"># editor contains a very long line that occupies last two lines of screen</span>
+<span id="L3727" class="LineNr">3727 </span>  <span class="Comment"># and still has something left over</span>
+<span id="L3728" class="LineNr">3728 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3729" class="LineNr">3729 </span><span class="Constant">bcdefgh]</span>
+<span id="L3730" class="LineNr">3730 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L3731" class="LineNr">3731 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3732" class="LineNr">3732 </span>  <span class="Comment"># some part of last line is not displayed</span>
+<span id="L3733" class="LineNr">3733 </span>  screen-should-contain [
+<span id="L3734" class="LineNr">3734 </span>   <span class="Constant"> .          .</span>
+<span id="L3735" class="LineNr">3735 </span>   <span class="Constant"> .a         .</span>
 <span id="L3736" class="LineNr">3736 </span>   <span class="Constant"> .bcd↩      .</span>
 <span id="L3737" class="LineNr">3737 </span>   <span class="Constant"> .efg↩      .</span>
-<span id="L3738" class="LineNr">3738 </span>   <span class="Constant"> .h         .</span>
-<span id="L3739" class="LineNr">3739 </span>  ]
-<span id="L3740" class="LineNr">3740 </span>]
-<span id="L3741" class="LineNr">3741 </span>
-<span id="L3742" class="LineNr">3742 </span><span class="Comment"># ctrl-b/page-up - render previous page if it exists</span>
-<span id="L3743" class="LineNr">3743 </span>
-<span id="L3744" class="LineNr">3744 </span><span class="muScenario">scenario</span> editor-can-scroll-up [
-<span id="L3745" class="LineNr">3745 </span>  <span class="Constant">local-scope</span>
-<span id="L3746" class="LineNr">3746 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3747" class="LineNr">3747 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3748" class="LineNr">3748 </span><span class="Constant">b</span>
-<span id="L3749" class="LineNr">3749 </span><span class="Constant">c</span>
-<span id="L3750" class="LineNr">3750 </span><span class="Constant">d]</span>
-<span id="L3751" class="LineNr">3751 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3752" class="LineNr">3752 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3753" class="LineNr">3753 </span>  screen-should-contain [
-<span id="L3754" class="LineNr">3754 </span>   <span class="Constant"> .          .</span>
-<span id="L3755" class="LineNr">3755 </span>   <span class="Constant"> .a         .</span>
-<span id="L3756" class="LineNr">3756 </span>   <span class="Constant"> .b         .</span>
-<span id="L3757" class="LineNr">3757 </span>   <span class="Constant"> .c         .</span>
-<span id="L3758" class="LineNr">3758 </span>  ]
-<span id="L3759" class="LineNr">3759 </span>  <span class="Comment"># scroll down</span>
-<span id="L3760" class="LineNr">3760 </span>  assume-console [
-<span id="L3761" class="LineNr">3761 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3762" class="LineNr">3762 </span>  ]
-<span id="L3763" class="LineNr">3763 </span>  run [
-<span id="L3764" class="LineNr">3764 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3765" class="LineNr">3765 </span>  ]
-<span id="L3766" class="LineNr">3766 </span>  <span class="Comment"># screen shows next page</span>
-<span id="L3767" class="LineNr">3767 </span>  screen-should-contain [
-<span id="L3768" class="LineNr">3768 </span>   <span class="Constant"> .          .</span>
-<span id="L3769" class="LineNr">3769 </span>   <span class="Constant"> .c         .</span>
-<span id="L3770" class="LineNr">3770 </span>   <span class="Constant"> .d         .</span>
-<span id="L3771" class="LineNr">3771 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
-<span id="L3772" class="LineNr">3772 </span>  ]
-<span id="L3773" class="LineNr">3773 </span>  <span class="Comment"># scroll back up</span>
-<span id="L3774" class="LineNr">3774 </span>  assume-console [
-<span id="L3775" class="LineNr">3775 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
-<span id="L3776" class="LineNr">3776 </span>  ]
-<span id="L3777" class="LineNr">3777 </span>  run [
-<span id="L3778" class="LineNr">3778 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3779" class="LineNr">3779 </span>  ]
-<span id="L3780" class="LineNr">3780 </span>  <span class="Comment"># screen shows original page again</span>
-<span id="L3781" class="LineNr">3781 </span>  screen-should-contain [
-<span id="L3782" class="LineNr">3782 </span>   <span class="Constant"> .          .</span>
-<span id="L3783" class="LineNr">3783 </span>   <span class="Constant"> .a         .</span>
-<span id="L3784" class="LineNr">3784 </span>   <span class="Constant"> .b         .</span>
-<span id="L3785" class="LineNr">3785 </span>   <span class="Constant"> .c         .</span>
-<span id="L3786" class="LineNr">3786 </span>  ]
-<span id="L3787" class="LineNr">3787 </span>]
-<span id="L3788" class="LineNr">3788 </span>
-<span id="L3789" class="LineNr">3789 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
-<span id="L3790" class="LineNr">3790 </span>  <span class="Delimiter">{</span>
-<span id="L3791" class="LineNr">3791 </span>    page-up?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">2/ctrl-b</span>
-<span id="L3792" class="LineNr">3792 </span>    <span class="muControl">break-unless</span> page-up?
-<span id="L3793" class="LineNr">3793 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3794" class="LineNr">3794 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L3795" class="LineNr">3795 </span>    editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L3820'>page-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L3796" class="LineNr">3796 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
-<span id="L3797" class="LineNr">3797 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L3798" class="LineNr">3798 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3799" class="LineNr">3799 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
-<span id="L3800" class="LineNr">3800 </span>   <span class="muControl"> return</span> movement?/go-render
-<span id="L3801" class="LineNr">3801 </span>  <span class="Delimiter">}</span>
-<span id="L3802" class="LineNr">3802 </span>]
-<span id="L3803" class="LineNr">3803 </span>
-<span id="L3804" class="LineNr">3804 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L199'>&lt;handle-special-key&gt;</a></span> [
-<span id="L3805" class="LineNr">3805 </span>  <span class="Delimiter">{</span>
-<span id="L3806" class="LineNr">3806 </span>    page-up?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65519/page-up</span>
-<span id="L3807" class="LineNr">3807 </span>    <span class="muControl">break-unless</span> page-up?
-<span id="L3808" class="LineNr">3808 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3809" class="LineNr">3809 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L3810" class="LineNr">3810 </span>    editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L3820'>page-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L3811" class="LineNr">3811 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
-<span id="L3812" class="LineNr">3812 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L3813" class="LineNr">3813 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3814" class="LineNr">3814 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
-<span id="L3815" class="LineNr">3815 </span>    <span class="Comment"># don't bother re-rendering if nothing changed. todo: test this</span>
-<span id="L3816" class="LineNr">3816 </span>   <span class="muControl"> return</span> movement?/go-render
-<span id="L3817" class="LineNr">3817 </span>  <span class="Delimiter">}</span>
-<span id="L3818" class="LineNr">3818 </span>]
-<span id="L3819" class="LineNr">3819 </span>
-<span id="L3820" class="LineNr">3820 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3820'>page-up</a> editor:&amp;:editor, <a href='../081print.mu.html#L782'>screen-height</a>:num<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
-<span id="L3821" class="LineNr">3821 </span>  <span class="Constant">local-scope</span>
-<span id="L3822" class="LineNr">3822 </span>  <span class="Constant">load-inputs</span>
-<span id="L3823" class="LineNr">3823 </span>  max:num <span class="Special">&lt;-</span> subtract <a href='../081print.mu.html#L782'>screen-height</a>, <span class="Constant">1/menu-bar</span>, <span class="Constant">1/overlapping-line</span>
-<span id="L3824" class="LineNr">3824 </span>  count:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
-<span id="L3825" class="LineNr">3825 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L3826" class="LineNr">3826 </span>  <span class="Delimiter">{</span>
-<span id="L3827" class="LineNr">3827 </span>    done?:bool <span class="Special">&lt;-</span> greater-or-equal count, max
-<span id="L3828" class="LineNr">3828 </span>    <span class="muControl">break-if</span> done?
-<span id="L3829" class="LineNr">3829 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> top-of-screen, editor
-<span id="L3830" class="LineNr">3830 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L3831" class="LineNr">3831 </span>    top-of-screen <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L32'>prev</a>
-<span id="L3832" class="LineNr">3832 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
-<span id="L3833" class="LineNr">3833 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
-<span id="L3834" class="LineNr">3834 </span>   <span class="muControl"> loop</span>
-<span id="L3835" class="LineNr">3835 </span>  <span class="Delimiter">}</span>
-<span id="L3836" class="LineNr">3836 </span>]
-<span id="L3837" class="LineNr">3837 </span>
-<span id="L3838" class="LineNr">3838 </span><span class="muScenario">scenario</span> editor-can-scroll-up-multiple-pages [
-<span id="L3839" class="LineNr">3839 </span>  <span class="Constant">local-scope</span>
-<span id="L3840" class="LineNr">3840 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
-<span id="L3841" class="LineNr">3841 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3842" class="LineNr">3842 </span>  <span class="Comment"># initialize editor with 8 lines</span>
-<span id="L3843" class="LineNr">3843 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3844" class="LineNr">3844 </span><span class="Constant">b</span>
-<span id="L3845" class="LineNr">3845 </span><span class="Constant">c</span>
-<span id="L3846" class="LineNr">3846 </span><span class="Constant">d</span>
-<span id="L3847" class="LineNr">3847 </span><span class="Constant">e</span>
-<span id="L3848" class="LineNr">3848 </span><span class="Constant">f</span>
-<span id="L3849" class="LineNr">3849 </span><span class="Constant">g</span>
-<span id="L3850" class="LineNr">3850 </span><span class="Constant">h]</span>
-<span id="L3851" class="LineNr">3851 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L3852" class="LineNr">3852 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3853" class="LineNr">3853 </span>  screen-should-contain [
-<span id="L3854" class="LineNr">3854 </span>   <span class="Constant"> .          .</span>
-<span id="L3855" class="LineNr">3855 </span>   <span class="Constant"> .a         .</span>
-<span id="L3856" class="LineNr">3856 </span>   <span class="Constant"> .b         .</span>
-<span id="L3857" class="LineNr">3857 </span>   <span class="Constant"> .c         .</span>
-<span id="L3858" class="LineNr">3858 </span>  ]
-<span id="L3859" class="LineNr">3859 </span>  <span class="Comment"># scroll down two pages</span>
-<span id="L3860" class="LineNr">3860 </span>  assume-console [
-<span id="L3861" class="LineNr">3861 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3862" class="LineNr">3862 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3863" class="LineNr">3863 </span>  ]
-<span id="L3864" class="LineNr">3864 </span>  run [
-<span id="L3865" class="LineNr">3865 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3866" class="LineNr">3866 </span>  ]
-<span id="L3867" class="LineNr">3867 </span>  <span class="Comment"># screen shows third page</span>
-<span id="L3868" class="LineNr">3868 </span>  screen-should-contain [
-<span id="L3869" class="LineNr">3869 </span>   <span class="Constant"> .          .</span>
-<span id="L3870" class="LineNr">3870 </span>   <span class="Constant"> .e         .</span>
-<span id="L3871" class="LineNr">3871 </span>   <span class="Constant"> .f         .</span>
-<span id="L3872" class="LineNr">3872 </span>   <span class="Constant"> .g         .</span>
-<span id="L3873" class="LineNr">3873 </span>  ]
-<span id="L3874" class="LineNr">3874 </span>  <span class="Comment"># scroll up</span>
-<span id="L3875" class="LineNr">3875 </span>  assume-console [
-<span id="L3876" class="LineNr">3876 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
-<span id="L3877" class="LineNr">3877 </span>  ]
-<span id="L3878" class="LineNr">3878 </span>  run [
-<span id="L3879" class="LineNr">3879 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3880" class="LineNr">3880 </span>  ]
-<span id="L3881" class="LineNr">3881 </span>  <span class="Comment"># screen shows second page</span>
-<span id="L3882" class="LineNr">3882 </span>  screen-should-contain [
-<span id="L3883" class="LineNr">3883 </span>   <span class="Constant"> .          .</span>
-<span id="L3884" class="LineNr">3884 </span>   <span class="Constant"> .c         .</span>
-<span id="L3885" class="LineNr">3885 </span>   <span class="Constant"> .d         .</span>
-<span id="L3886" class="LineNr">3886 </span>   <span class="Constant"> .e         .</span>
-<span id="L3887" class="LineNr">3887 </span>  ]
-<span id="L3888" class="LineNr">3888 </span>  <span class="Comment"># scroll up again</span>
-<span id="L3889" class="LineNr">3889 </span>  assume-console [
-<span id="L3890" class="LineNr">3890 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
-<span id="L3891" class="LineNr">3891 </span>  ]
-<span id="L3892" class="LineNr">3892 </span>  run [
-<span id="L3893" class="LineNr">3893 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3894" class="LineNr">3894 </span>  ]
-<span id="L3895" class="LineNr">3895 </span>  <span class="Comment"># screen shows original page again</span>
-<span id="L3896" class="LineNr">3896 </span>  screen-should-contain [
-<span id="L3897" class="LineNr">3897 </span>   <span class="Constant"> .          .</span>
-<span id="L3898" class="LineNr">3898 </span>   <span class="Constant"> .a         .</span>
-<span id="L3899" class="LineNr">3899 </span>   <span class="Constant"> .b         .</span>
-<span id="L3900" class="LineNr">3900 </span>   <span class="Constant"> .c         .</span>
-<span id="L3901" class="LineNr">3901 </span>  ]
-<span id="L3902" class="LineNr">3902 </span>]
-<span id="L3903" class="LineNr">3903 </span>
-<span id="L3904" class="LineNr">3904 </span><span class="muScenario">scenario</span> editor-can-scroll-up-wrapped-lines [
-<span id="L3905" class="LineNr">3905 </span>  <span class="Constant">local-scope</span>
-<span id="L3906" class="LineNr">3906 </span>  <span class="Comment"># screen has 1 line for menu + 5 lines for text</span>
-<span id="L3907" class="LineNr">3907 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">6/height</span>
-<span id="L3908" class="LineNr">3908 </span>  <span class="Comment"># editor contains a long line in the first page</span>
-<span id="L3909" class="LineNr">3909 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3910" class="LineNr">3910 </span><span class="Constant">b</span>
-<span id="L3911" class="LineNr">3911 </span><span class="Constant">cdefgh</span>
-<span id="L3912" class="LineNr">3912 </span><span class="Constant">i</span>
-<span id="L3913" class="LineNr">3913 </span><span class="Constant">j</span>
-<span id="L3914" class="LineNr">3914 </span><span class="Constant">k</span>
-<span id="L3915" class="LineNr">3915 </span><span class="Constant">l</span>
-<span id="L3916" class="LineNr">3916 </span><span class="Constant">m</span>
-<span id="L3917" class="LineNr">3917 </span><span class="Constant">n</span>
-<span id="L3918" class="LineNr">3918 </span><span class="Constant">o]</span>
-<span id="L3919" class="LineNr">3919 </span>  <span class="Comment"># editor screen triggers wrap of last line</span>
-<span id="L3920" class="LineNr">3920 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L3921" class="LineNr">3921 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3922" class="LineNr">3922 </span>  <span class="Comment"># some part of last line is not displayed</span>
-<span id="L3923" class="LineNr">3923 </span>  screen-should-contain [
-<span id="L3924" class="LineNr">3924 </span>   <span class="Constant"> .          .</span>
-<span id="L3925" class="LineNr">3925 </span>   <span class="Constant"> .a         .</span>
-<span id="L3926" class="LineNr">3926 </span>   <span class="Constant"> .b         .</span>
-<span id="L3927" class="LineNr">3927 </span>   <span class="Constant"> .cde↩      .</span>
-<span id="L3928" class="LineNr">3928 </span>   <span class="Constant"> .fgh       .</span>
-<span id="L3929" class="LineNr">3929 </span>   <span class="Constant"> .i         .</span>
-<span id="L3930" class="LineNr">3930 </span>  ]
-<span id="L3931" class="LineNr">3931 </span>  <span class="Comment"># scroll down a page and a line</span>
-<span id="L3932" class="LineNr">3932 </span>  assume-console [
-<span id="L3933" class="LineNr">3933 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3934" class="LineNr">3934 </span>    left-click<span class="Constant"> 5</span>,<span class="Constant"> 0</span>
-<span id="L3935" class="LineNr">3935 </span>    press down-arrow
-<span id="L3936" class="LineNr">3936 </span>  ]
-<span id="L3937" class="LineNr">3937 </span>  run [
-<span id="L3938" class="LineNr">3938 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3939" class="LineNr">3939 </span>  ]
-<span id="L3940" class="LineNr">3940 </span>  <span class="Comment"># screen shows entire wrapped line</span>
-<span id="L3941" class="LineNr">3941 </span>  screen-should-contain [
-<span id="L3942" class="LineNr">3942 </span>   <span class="Constant"> .          .</span>
-<span id="L3943" class="LineNr">3943 </span>   <span class="Constant"> .j         .</span>
-<span id="L3944" class="LineNr">3944 </span>   <span class="Constant"> .k         .</span>
-<span id="L3945" class="LineNr">3945 </span>   <span class="Constant"> .l         .</span>
-<span id="L3946" class="LineNr">3946 </span>   <span class="Constant"> .m         .</span>
-<span id="L3947" class="LineNr">3947 </span>   <span class="Constant"> .n         .</span>
-<span id="L3948" class="LineNr">3948 </span>  ]
-<span id="L3949" class="LineNr">3949 </span>  <span class="Comment"># now scroll up one page</span>
-<span id="L3950" class="LineNr">3950 </span>  assume-console [
-<span id="L3951" class="LineNr">3951 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L3738" class="LineNr">3738 </span>  ]
+<span id="L3739" class="LineNr">3739 </span>  <span class="Comment"># scroll down</span>
+<span id="L3740" class="LineNr">3740 </span>  assume-console [
+<span id="L3741" class="LineNr">3741 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3742" class="LineNr">3742 </span>  ]
+<span id="L3743" class="LineNr">3743 </span>  run [
+<span id="L3744" class="LineNr">3744 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3745" class="LineNr">3745 </span>  ]
+<span id="L3746" class="LineNr">3746 </span>  <span class="Comment"># screen shows entire wrapped line</span>
+<span id="L3747" class="LineNr">3747 </span>  screen-should-contain [
+<span id="L3748" class="LineNr">3748 </span>   <span class="Constant"> .          .</span>
+<span id="L3749" class="LineNr">3749 </span>   <span class="Constant"> .bcd↩      .</span>
+<span id="L3750" class="LineNr">3750 </span>   <span class="Constant"> .efg↩      .</span>
+<span id="L3751" class="LineNr">3751 </span>   <span class="Constant"> .h         .</span>
+<span id="L3752" class="LineNr">3752 </span>  ]
+<span id="L3753" class="LineNr">3753 </span>]
+<span id="L3754" class="LineNr">3754 </span>
+<span id="L3755" class="LineNr">3755 </span><span class="Comment"># ctrl-b/page-up - render previous page if it exists</span>
+<span id="L3756" class="LineNr">3756 </span>
+<span id="L3757" class="LineNr">3757 </span><span class="muScenario">scenario</span> editor-can-scroll-up [
+<span id="L3758" class="LineNr">3758 </span>  <span class="Constant">local-scope</span>
+<span id="L3759" class="LineNr">3759 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3760" class="LineNr">3760 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3761" class="LineNr">3761 </span><span class="Constant">b</span>
+<span id="L3762" class="LineNr">3762 </span><span class="Constant">c</span>
+<span id="L3763" class="LineNr">3763 </span><span class="Constant">d]</span>
+<span id="L3764" class="LineNr">3764 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3765" class="LineNr">3765 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3766" class="LineNr">3766 </span>  screen-should-contain [
+<span id="L3767" class="LineNr">3767 </span>   <span class="Constant"> .          .</span>
+<span id="L3768" class="LineNr">3768 </span>   <span class="Constant"> .a         .</span>
+<span id="L3769" class="LineNr">3769 </span>   <span class="Constant"> .b         .</span>
+<span id="L3770" class="LineNr">3770 </span>   <span class="Constant"> .c         .</span>
+<span id="L3771" class="LineNr">3771 </span>  ]
+<span id="L3772" class="LineNr">3772 </span>  <span class="Comment"># scroll down</span>
+<span id="L3773" class="LineNr">3773 </span>  assume-console [
+<span id="L3774" class="LineNr">3774 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3775" class="LineNr">3775 </span>  ]
+<span id="L3776" class="LineNr">3776 </span>  run [
+<span id="L3777" class="LineNr">3777 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3778" class="LineNr">3778 </span>  ]
+<span id="L3779" class="LineNr">3779 </span>  <span class="Comment"># screen shows next page</span>
+<span id="L3780" class="LineNr">3780 </span>  screen-should-contain [
+<span id="L3781" class="LineNr">3781 </span>   <span class="Constant"> .          .</span>
+<span id="L3782" class="LineNr">3782 </span>   <span class="Constant"> .c         .</span>
+<span id="L3783" class="LineNr">3783 </span>   <span class="Constant"> .d         .</span>
+<span id="L3784" class="LineNr">3784 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L3785" class="LineNr">3785 </span>  ]
+<span id="L3786" class="LineNr">3786 </span>  <span class="Comment"># scroll back up</span>
+<span id="L3787" class="LineNr">3787 </span>  assume-console [
+<span id="L3788" class="LineNr">3788 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L3789" class="LineNr">3789 </span>  ]
+<span id="L3790" class="LineNr">3790 </span>  run [
+<span id="L3791" class="LineNr">3791 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3792" class="LineNr">3792 </span>  ]
+<span id="L3793" class="LineNr">3793 </span>  <span class="Comment"># screen shows original page again</span>
+<span id="L3794" class="LineNr">3794 </span>  screen-should-contain [
+<span id="L3795" class="LineNr">3795 </span>   <span class="Constant"> .          .</span>
+<span id="L3796" class="LineNr">3796 </span>   <span class="Constant"> .a         .</span>
+<span id="L3797" class="LineNr">3797 </span>   <span class="Constant"> .b         .</span>
+<span id="L3798" class="LineNr">3798 </span>   <span class="Constant"> .c         .</span>
+<span id="L3799" class="LineNr">3799 </span>  ]
+<span id="L3800" class="LineNr">3800 </span>]
+<span id="L3801" class="LineNr">3801 </span>
+<span id="L3802" class="LineNr">3802 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L3803" class="LineNr">3803 </span>  <span class="Delimiter">{</span>
+<span id="L3804" class="LineNr">3804 </span>    page-up?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">2/ctrl-b</span>
+<span id="L3805" class="LineNr">3805 </span>    <span class="muControl">break-unless</span> page-up?
+<span id="L3806" class="LineNr">3806 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3807" class="LineNr">3807 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L3808" class="LineNr">3808 </span>    editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L3833'>page-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L3809" class="LineNr">3809 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
+<span id="L3810" class="LineNr">3810 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L3811" class="LineNr">3811 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3812" class="LineNr">3812 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
+<span id="L3813" class="LineNr">3813 </span>   <span class="muControl"> return</span> movement?/go-render
+<span id="L3814" class="LineNr">3814 </span>  <span class="Delimiter">}</span>
+<span id="L3815" class="LineNr">3815 </span>]
+<span id="L3816" class="LineNr">3816 </span>
+<span id="L3817" class="LineNr">3817 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L199'>&lt;handle-special-key&gt;</a></span> [
+<span id="L3818" class="LineNr">3818 </span>  <span class="Delimiter">{</span>
+<span id="L3819" class="LineNr">3819 </span>    page-up?:bool <span class="Special">&lt;-</span> equal k, <span class="Constant">65519/page-up</span>
+<span id="L3820" class="LineNr">3820 </span>    <span class="muControl">break-unless</span> page-up?
+<span id="L3821" class="LineNr">3821 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3822" class="LineNr">3822 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L3823" class="LineNr">3823 </span>    editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L3833'>page-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L3824" class="LineNr">3824 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
+<span id="L3825" class="LineNr">3825 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L3826" class="LineNr">3826 </span>    top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3827" class="LineNr">3827 </span>    movement?:bool <span class="Special">&lt;-</span> not-equal top-of-screen, old-top
+<span id="L3828" class="LineNr">3828 </span>    <span class="Comment"># don't bother re-rendering if nothing changed. todo: test this</span>
+<span id="L3829" class="LineNr">3829 </span>   <span class="muControl"> return</span> movement?/go-render
+<span id="L3830" class="LineNr">3830 </span>  <span class="Delimiter">}</span>
+<span id="L3831" class="LineNr">3831 </span>]
+<span id="L3832" class="LineNr">3832 </span>
+<span id="L3833" class="LineNr">3833 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L3833'>page-up</a> editor:&amp;:editor, <a href='../081print.mu.html#L782'>screen-height</a>:num<span class="muRecipe"> -&gt; </span>editor:&amp;:editor [
+<span id="L3834" class="LineNr">3834 </span>  <span class="Constant">local-scope</span>
+<span id="L3835" class="LineNr">3835 </span>  <span class="Constant">load-inputs</span>
+<span id="L3836" class="LineNr">3836 </span>  max:num <span class="Special">&lt;-</span> subtract <a href='../081print.mu.html#L782'>screen-height</a>, <span class="Constant">1/menu-bar</span>, <span class="Constant">1/overlapping-line</span>
+<span id="L3837" class="LineNr">3837 </span>  count:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
+<span id="L3838" class="LineNr">3838 </span>  top-of-screen:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L3839" class="LineNr">3839 </span>  <span class="Delimiter">{</span>
+<span id="L3840" class="LineNr">3840 </span>    done?:bool <span class="Special">&lt;-</span> greater-or-equal count, max
+<span id="L3841" class="LineNr">3841 </span>    <span class="muControl">break-if</span> done?
+<span id="L3842" class="LineNr">3842 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> top-of-screen, editor
+<span id="L3843" class="LineNr">3843 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L3844" class="LineNr">3844 </span>    top-of-screen <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L38'>prev</a>
+<span id="L3845" class="LineNr">3845 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, top-of-screen
+<span id="L3846" class="LineNr">3846 </span>    count <span class="Special">&lt;-</span> add count,<span class="Constant"> 1</span>
+<span id="L3847" class="LineNr">3847 </span>   <span class="muControl"> loop</span>
+<span id="L3848" class="LineNr">3848 </span>  <span class="Delimiter">}</span>
+<span id="L3849" class="LineNr">3849 </span>]
+<span id="L3850" class="LineNr">3850 </span>
+<span id="L3851" class="LineNr">3851 </span><span class="muScenario">scenario</span> editor-can-scroll-up-multiple-pages [
+<span id="L3852" class="LineNr">3852 </span>  <span class="Constant">local-scope</span>
+<span id="L3853" class="LineNr">3853 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines</span>
+<span id="L3854" class="LineNr">3854 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3855" class="LineNr">3855 </span>  <span class="Comment"># initialize editor with 8 lines</span>
+<span id="L3856" class="LineNr">3856 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3857" class="LineNr">3857 </span><span class="Constant">b</span>
+<span id="L3858" class="LineNr">3858 </span><span class="Constant">c</span>
+<span id="L3859" class="LineNr">3859 </span><span class="Constant">d</span>
+<span id="L3860" class="LineNr">3860 </span><span class="Constant">e</span>
+<span id="L3861" class="LineNr">3861 </span><span class="Constant">f</span>
+<span id="L3862" class="LineNr">3862 </span><span class="Constant">g</span>
+<span id="L3863" class="LineNr">3863 </span><span class="Constant">h]</span>
+<span id="L3864" class="LineNr">3864 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
+<span id="L3865" class="LineNr">3865 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3866" class="LineNr">3866 </span>  screen-should-contain [
+<span id="L3867" class="LineNr">3867 </span>   <span class="Constant"> .          .</span>
+<span id="L3868" class="LineNr">3868 </span>   <span class="Constant"> .a         .</span>
+<span id="L3869" class="LineNr">3869 </span>   <span class="Constant"> .b         .</span>
+<span id="L3870" class="LineNr">3870 </span>   <span class="Constant"> .c         .</span>
+<span id="L3871" class="LineNr">3871 </span>  ]
+<span id="L3872" class="LineNr">3872 </span>  <span class="Comment"># scroll down two pages</span>
+<span id="L3873" class="LineNr">3873 </span>  assume-console [
+<span id="L3874" class="LineNr">3874 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3875" class="LineNr">3875 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3876" class="LineNr">3876 </span>  ]
+<span id="L3877" class="LineNr">3877 </span>  run [
+<span id="L3878" class="LineNr">3878 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3879" class="LineNr">3879 </span>  ]
+<span id="L3880" class="LineNr">3880 </span>  <span class="Comment"># screen shows third page</span>
+<span id="L3881" class="LineNr">3881 </span>  screen-should-contain [
+<span id="L3882" class="LineNr">3882 </span>   <span class="Constant"> .          .</span>
+<span id="L3883" class="LineNr">3883 </span>   <span class="Constant"> .e         .</span>
+<span id="L3884" class="LineNr">3884 </span>   <span class="Constant"> .f         .</span>
+<span id="L3885" class="LineNr">3885 </span>   <span class="Constant"> .g         .</span>
+<span id="L3886" class="LineNr">3886 </span>  ]
+<span id="L3887" class="LineNr">3887 </span>  <span class="Comment"># scroll up</span>
+<span id="L3888" class="LineNr">3888 </span>  assume-console [
+<span id="L3889" class="LineNr">3889 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L3890" class="LineNr">3890 </span>  ]
+<span id="L3891" class="LineNr">3891 </span>  run [
+<span id="L3892" class="LineNr">3892 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3893" class="LineNr">3893 </span>  ]
+<span id="L3894" class="LineNr">3894 </span>  <span class="Comment"># screen shows second page</span>
+<span id="L3895" class="LineNr">3895 </span>  screen-should-contain [
+<span id="L3896" class="LineNr">3896 </span>   <span class="Constant"> .          .</span>
+<span id="L3897" class="LineNr">3897 </span>   <span class="Constant"> .c         .</span>
+<span id="L3898" class="LineNr">3898 </span>   <span class="Constant"> .d         .</span>
+<span id="L3899" class="LineNr">3899 </span>   <span class="Constant"> .e         .</span>
+<span id="L3900" class="LineNr">3900 </span>  ]
+<span id="L3901" class="LineNr">3901 </span>  <span class="Comment"># scroll up again</span>
+<span id="L3902" class="LineNr">3902 </span>  assume-console [
+<span id="L3903" class="LineNr">3903 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L3904" class="LineNr">3904 </span>  ]
+<span id="L3905" class="LineNr">3905 </span>  run [
+<span id="L3906" class="LineNr">3906 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3907" class="LineNr">3907 </span>  ]
+<span id="L3908" class="LineNr">3908 </span>  <span class="Comment"># screen shows original page again</span>
+<span id="L3909" class="LineNr">3909 </span>  screen-should-contain [
+<span id="L3910" class="LineNr">3910 </span>   <span class="Constant"> .          .</span>
+<span id="L3911" class="LineNr">3911 </span>   <span class="Constant"> .a         .</span>
+<span id="L3912" class="LineNr">3912 </span>   <span class="Constant"> .b         .</span>
+<span id="L3913" class="LineNr">3913 </span>   <span class="Constant"> .c         .</span>
+<span id="L3914" class="LineNr">3914 </span>  ]
+<span id="L3915" class="LineNr">3915 </span>]
+<span id="L3916" class="LineNr">3916 </span>
+<span id="L3917" class="LineNr">3917 </span><span class="muScenario">scenario</span> editor-can-scroll-up-wrapped-lines [
+<span id="L3918" class="LineNr">3918 </span>  <span class="Constant">local-scope</span>
+<span id="L3919" class="LineNr">3919 </span>  <span class="Comment"># screen has 1 line for menu + 5 lines for text</span>
+<span id="L3920" class="LineNr">3920 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">6/height</span>
+<span id="L3921" class="LineNr">3921 </span>  <span class="Comment"># editor contains a long line in the first page</span>
+<span id="L3922" class="LineNr">3922 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3923" class="LineNr">3923 </span><span class="Constant">b</span>
+<span id="L3924" class="LineNr">3924 </span><span class="Constant">cdefgh</span>
+<span id="L3925" class="LineNr">3925 </span><span class="Constant">i</span>
+<span id="L3926" class="LineNr">3926 </span><span class="Constant">j</span>
+<span id="L3927" class="LineNr">3927 </span><span class="Constant">k</span>
+<span id="L3928" class="LineNr">3928 </span><span class="Constant">l</span>
+<span id="L3929" class="LineNr">3929 </span><span class="Constant">m</span>
+<span id="L3930" class="LineNr">3930 </span><span class="Constant">n</span>
+<span id="L3931" class="LineNr">3931 </span><span class="Constant">o]</span>
+<span id="L3932" class="LineNr">3932 </span>  <span class="Comment"># editor screen triggers wrap of last line</span>
+<span id="L3933" class="LineNr">3933 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L3934" class="LineNr">3934 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3935" class="LineNr">3935 </span>  <span class="Comment"># some part of last line is not displayed</span>
+<span id="L3936" class="LineNr">3936 </span>  screen-should-contain [
+<span id="L3937" class="LineNr">3937 </span>   <span class="Constant"> .          .</span>
+<span id="L3938" class="LineNr">3938 </span>   <span class="Constant"> .a         .</span>
+<span id="L3939" class="LineNr">3939 </span>   <span class="Constant"> .b         .</span>
+<span id="L3940" class="LineNr">3940 </span>   <span class="Constant"> .cde↩      .</span>
+<span id="L3941" class="LineNr">3941 </span>   <span class="Constant"> .fgh       .</span>
+<span id="L3942" class="LineNr">3942 </span>   <span class="Constant"> .i         .</span>
+<span id="L3943" class="LineNr">3943 </span>  ]
+<span id="L3944" class="LineNr">3944 </span>  <span class="Comment"># scroll down a page and a line</span>
+<span id="L3945" class="LineNr">3945 </span>  assume-console [
+<span id="L3946" class="LineNr">3946 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L3947" class="LineNr">3947 </span>    left-click<span class="Constant"> 5</span>,<span class="Constant"> 0</span>
+<span id="L3948" class="LineNr">3948 </span>    press down-arrow
+<span id="L3949" class="LineNr">3949 </span>  ]
+<span id="L3950" class="LineNr">3950 </span>  run [
+<span id="L3951" class="LineNr">3951 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L3952" class="LineNr">3952 </span>  ]
-<span id="L3953" class="LineNr">3953 </span>  run [
-<span id="L3954" class="LineNr">3954 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3955" class="LineNr">3955 </span>  ]
-<span id="L3956" class="LineNr">3956 </span>  <span class="Comment"># screen resets</span>
-<span id="L3957" class="LineNr">3957 </span>  screen-should-contain [
-<span id="L3958" class="LineNr">3958 </span>   <span class="Constant"> .          .</span>
-<span id="L3959" class="LineNr">3959 </span>   <span class="Constant"> .b         .</span>
-<span id="L3960" class="LineNr">3960 </span>   <span class="Constant"> .cde↩      .</span>
-<span id="L3961" class="LineNr">3961 </span>   <span class="Constant"> .fgh       .</span>
-<span id="L3962" class="LineNr">3962 </span>   <span class="Constant"> .i         .</span>
-<span id="L3963" class="LineNr">3963 </span>   <span class="Constant"> .j         .</span>
-<span id="L3964" class="LineNr">3964 </span>  ]
-<span id="L3965" class="LineNr">3965 </span>]
-<span id="L3966" class="LineNr">3966 </span>
-<span id="L3967" class="LineNr">3967 </span><span class="muScenario">scenario</span> editor-can-scroll-up-wrapped-lines-2 [
-<span id="L3968" class="LineNr">3968 </span>  <span class="Constant">local-scope</span>
-<span id="L3969" class="LineNr">3969 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
-<span id="L3970" class="LineNr">3970 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L3971" class="LineNr">3971 </span>  <span class="Comment"># editor contains a very long line that occupies last two lines of screen</span>
-<span id="L3972" class="LineNr">3972 </span>  <span class="Comment"># and still has something left over</span>
-<span id="L3973" class="LineNr">3973 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
-<span id="L3974" class="LineNr">3974 </span><span class="Constant">bcdefgh]</span>
-<span id="L3975" class="LineNr">3975 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L3976" class="LineNr">3976 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L3977" class="LineNr">3977 </span>  <span class="Comment"># some part of last line is not displayed</span>
-<span id="L3978" class="LineNr">3978 </span>  screen-should-contain [
-<span id="L3979" class="LineNr">3979 </span>   <span class="Constant"> .          .</span>
-<span id="L3980" class="LineNr">3980 </span>   <span class="Constant"> .a         .</span>
-<span id="L3981" class="LineNr">3981 </span>   <span class="Constant"> .bcd↩      .</span>
-<span id="L3982" class="LineNr">3982 </span>   <span class="Constant"> .efg↩      .</span>
-<span id="L3983" class="LineNr">3983 </span>  ]
-<span id="L3984" class="LineNr">3984 </span>  <span class="Comment"># scroll down</span>
-<span id="L3985" class="LineNr">3985 </span>  assume-console [
-<span id="L3986" class="LineNr">3986 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L3987" class="LineNr">3987 </span>  ]
-<span id="L3988" class="LineNr">3988 </span>  run [
-<span id="L3989" class="LineNr">3989 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L3990" class="LineNr">3990 </span>  ]
-<span id="L3991" class="LineNr">3991 </span>  <span class="Comment"># screen shows entire wrapped line</span>
-<span id="L3992" class="LineNr">3992 </span>  screen-should-contain [
-<span id="L3993" class="LineNr">3993 </span>   <span class="Constant"> .          .</span>
+<span id="L3953" class="LineNr">3953 </span>  <span class="Comment"># screen shows entire wrapped line</span>
+<span id="L3954" class="LineNr">3954 </span>  screen-should-contain [
+<span id="L3955" class="LineNr">3955 </span>   <span class="Constant"> .          .</span>
+<span id="L3956" class="LineNr">3956 </span>   <span class="Constant"> .j         .</span>
+<span id="L3957" class="LineNr">3957 </span>   <span class="Constant"> .k         .</span>
+<span id="L3958" class="LineNr">3958 </span>   <span class="Constant"> .l         .</span>
+<span id="L3959" class="LineNr">3959 </span>   <span class="Constant"> .m         .</span>
+<span id="L3960" class="LineNr">3960 </span>   <span class="Constant"> .n         .</span>
+<span id="L3961" class="LineNr">3961 </span>  ]
+<span id="L3962" class="LineNr">3962 </span>  <span class="Comment"># now scroll up one page</span>
+<span id="L3963" class="LineNr">3963 </span>  assume-console [
+<span id="L3964" class="LineNr">3964 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L3965" class="LineNr">3965 </span>  ]
+<span id="L3966" class="LineNr">3966 </span>  run [
+<span id="L3967" class="LineNr">3967 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L3968" class="LineNr">3968 </span>  ]
+<span id="L3969" class="LineNr">3969 </span>  <span class="Comment"># screen resets</span>
+<span id="L3970" class="LineNr">3970 </span>  screen-should-contain [
+<span id="L3971" class="LineNr">3971 </span>   <span class="Constant"> .          .</span>
+<span id="L3972" class="LineNr">3972 </span>   <span class="Constant"> .b         .</span>
+<span id="L3973" class="LineNr">3973 </span>   <span class="Constant"> .cde↩      .</span>
+<span id="L3974" class="LineNr">3974 </span>   <span class="Constant"> .fgh       .</span>
+<span id="L3975" class="LineNr">3975 </span>   <span class="Constant"> .i         .</span>
+<span id="L3976" class="LineNr">3976 </span>   <span class="Constant"> .j         .</span>
+<span id="L3977" class="LineNr">3977 </span>  ]
+<span id="L3978" class="LineNr">3978 </span>]
+<span id="L3979" class="LineNr">3979 </span>
+<span id="L3980" class="LineNr">3980 </span><span class="muScenario">scenario</span> editor-can-scroll-up-wrapped-lines-2 [
+<span id="L3981" class="LineNr">3981 </span>  <span class="Constant">local-scope</span>
+<span id="L3982" class="LineNr">3982 </span>  <span class="Comment"># screen has 1 line for menu + 3 lines for text</span>
+<span id="L3983" class="LineNr">3983 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L3984" class="LineNr">3984 </span>  <span class="Comment"># editor contains a very long line that occupies last two lines of screen</span>
+<span id="L3985" class="LineNr">3985 </span>  <span class="Comment"># and still has something left over</span>
+<span id="L3986" class="LineNr">3986 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[a</span>
+<span id="L3987" class="LineNr">3987 </span><span class="Constant">bcdefgh]</span>
+<span id="L3988" class="LineNr">3988 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L3989" class="LineNr">3989 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L3990" class="LineNr">3990 </span>  <span class="Comment"># some part of last line is not displayed</span>
+<span id="L3991" class="LineNr">3991 </span>  screen-should-contain [
+<span id="L3992" class="LineNr">3992 </span>   <span class="Constant"> .          .</span>
+<span id="L3993" class="LineNr">3993 </span>   <span class="Constant"> .a         .</span>
 <span id="L3994" class="LineNr">3994 </span>   <span class="Constant"> .bcd↩      .</span>
 <span id="L3995" class="LineNr">3995 </span>   <span class="Constant"> .efg↩      .</span>
-<span id="L3996" class="LineNr">3996 </span>   <span class="Constant"> .h         .</span>
-<span id="L3997" class="LineNr">3997 </span>  ]
-<span id="L3998" class="LineNr">3998 </span>  <span class="Comment"># scroll back up</span>
-<span id="L3999" class="LineNr">3999 </span>  assume-console [
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-<span id="L4001" class="LineNr">4001 </span>  ]
-<span id="L4002" class="LineNr">4002 </span>  run [
-<span id="L4003" class="LineNr">4003 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L4004" class="LineNr">4004 </span>  ]
-<span id="L4005" class="LineNr">4005 </span>  <span class="Comment"># screen resets</span>
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-<span id="L4007" class="LineNr">4007 </span>   <span class="Constant"> .          .</span>
-<span id="L4008" class="LineNr">4008 </span>   <span class="Constant"> .a         .</span>
-<span id="L4009" class="LineNr">4009 </span>   <span class="Constant"> .bcd↩      .</span>
-<span id="L4010" class="LineNr">4010 </span>   <span class="Constant"> .efg↩      .</span>
-<span id="L4011" class="LineNr">4011 </span>  ]
-<span id="L4012" class="LineNr">4012 </span>]
-<span id="L4013" class="LineNr">4013 </span>
-<span id="L4014" class="LineNr">4014 </span><span class="muScenario">scenario</span> editor-can-scroll-up-past-nonempty-lines [
-<span id="L4015" class="LineNr">4015 </span>  <span class="Constant">local-scope</span>
-<span id="L4016" class="LineNr">4016 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L4017" class="LineNr">4017 </span>  <span class="Comment"># text with empty line in second screen</span>
-<span id="L4018" class="LineNr">4018 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[axx</span>
-<span id="L4019" class="LineNr">4019 </span><span class="Constant">bxx</span>
-<span id="L4020" class="LineNr">4020 </span><span class="Constant">cxx</span>
-<span id="L4021" class="LineNr">4021 </span><span class="Constant">dxx</span>
-<span id="L4022" class="LineNr">4022 </span><span class="Constant">exx</span>
-<span id="L4023" class="LineNr">4023 </span><span class="Constant">fxx</span>
-<span id="L4024" class="LineNr">4024 </span><span class="Constant">gxx</span>
-<span id="L4025" class="LineNr">4025 </span><span class="Constant">hxx</span>
-<span id="L4026" class="LineNr">4026 </span><span class="Constant">]</span>
-<span id="L4027" class="LineNr">4027 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L4028" class="LineNr">4028 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L4029" class="LineNr">4029 </span>  screen-should-contain [
-<span id="L4030" class="LineNr">4030 </span>   <span class="Constant"> .          .</span>
-<span id="L4031" class="LineNr">4031 </span>   <span class="Constant"> .axx       .</span>
-<span id="L4032" class="LineNr">4032 </span>   <span class="Constant"> .bxx       .</span>
-<span id="L4033" class="LineNr">4033 </span>   <span class="Constant"> .cxx       .</span>
-<span id="L4034" class="LineNr">4034 </span>  ]
-<span id="L4035" class="LineNr">4035 </span>  assume-console [
-<span id="L4036" class="LineNr">4036 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L4037" class="LineNr">4037 </span>  ]
-<span id="L4038" class="LineNr">4038 </span>  run [
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-<span id="L4040" class="LineNr">4040 </span>  ]
-<span id="L4041" class="LineNr">4041 </span>  screen-should-contain [
-<span id="L4042" class="LineNr">4042 </span>   <span class="Constant"> .          .</span>
-<span id="L4043" class="LineNr">4043 </span>   <span class="Constant"> .cxx       .</span>
-<span id="L4044" class="LineNr">4044 </span>   <span class="Constant"> .dxx       .</span>
-<span id="L4045" class="LineNr">4045 </span>   <span class="Constant"> .exx       .</span>
-<span id="L4046" class="LineNr">4046 </span>  ]
-<span id="L4047" class="LineNr">4047 </span>  assume-console [
-<span id="L4048" class="LineNr">4048 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L4049" class="LineNr">4049 </span>  ]
-<span id="L4050" class="LineNr">4050 </span>  run [
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-<span id="L4052" class="LineNr">4052 </span>  ]
-<span id="L4053" class="LineNr">4053 </span>  screen-should-contain [
-<span id="L4054" class="LineNr">4054 </span>   <span class="Constant"> .          .</span>
-<span id="L4055" class="LineNr">4055 </span>   <span class="Constant"> .exx       .</span>
-<span id="L4056" class="LineNr">4056 </span>   <span class="Constant"> .fxx       .</span>
-<span id="L4057" class="LineNr">4057 </span>   <span class="Constant"> .gxx       .</span>
-<span id="L4058" class="LineNr">4058 </span>  ]
-<span id="L4059" class="LineNr">4059 </span>  <span class="Comment"># scroll back up past empty line</span>
+<span id="L3996" class="LineNr">3996 </span>  ]
+<span id="L3997" class="LineNr">3997 </span>  <span class="Comment"># scroll down</span>
+<span id="L3998" class="LineNr">3998 </span>  assume-console [
+<span id="L3999" class="LineNr">3999 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L4000" class="LineNr">4000 </span>  ]
+<span id="L4001" class="LineNr">4001 </span>  run [
+<span id="L4002" class="LineNr">4002 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4003" class="LineNr">4003 </span>  ]
+<span id="L4004" class="LineNr">4004 </span>  <span class="Comment"># screen shows entire wrapped line</span>
+<span id="L4005" class="LineNr">4005 </span>  screen-should-contain [
+<span id="L4006" class="LineNr">4006 </span>   <span class="Constant"> .          .</span>
+<span id="L4007" class="LineNr">4007 </span>   <span class="Constant"> .bcd↩      .</span>
+<span id="L4008" class="LineNr">4008 </span>   <span class="Constant"> .efg↩      .</span>
+<span id="L4009" class="LineNr">4009 </span>   <span class="Constant"> .h         .</span>
+<span id="L4010" class="LineNr">4010 </span>  ]
+<span id="L4011" class="LineNr">4011 </span>  <span class="Comment"># scroll back up</span>
+<span id="L4012" class="LineNr">4012 </span>  assume-console [
+<span id="L4013" class="LineNr">4013 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L4014" class="LineNr">4014 </span>  ]
+<span id="L4015" class="LineNr">4015 </span>  run [
+<span id="L4016" class="LineNr">4016 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4017" class="LineNr">4017 </span>  ]
+<span id="L4018" class="LineNr">4018 </span>  <span class="Comment"># screen resets</span>
+<span id="L4019" class="LineNr">4019 </span>  screen-should-contain [
+<span id="L4020" class="LineNr">4020 </span>   <span class="Constant"> .          .</span>
+<span id="L4021" class="LineNr">4021 </span>   <span class="Constant"> .a         .</span>
+<span id="L4022" class="LineNr">4022 </span>   <span class="Constant"> .bcd↩      .</span>
+<span id="L4023" class="LineNr">4023 </span>   <span class="Constant"> .efg↩      .</span>
+<span id="L4024" class="LineNr">4024 </span>  ]
+<span id="L4025" class="LineNr">4025 </span>]
+<span id="L4026" class="LineNr">4026 </span>
+<span id="L4027" class="LineNr">4027 </span><span class="muScenario">scenario</span> editor-can-scroll-up-past-nonempty-lines [
+<span id="L4028" class="LineNr">4028 </span>  <span class="Constant">local-scope</span>
+<span id="L4029" class="LineNr">4029 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L4030" class="LineNr">4030 </span>  <span class="Comment"># text with empty line in second screen</span>
+<span id="L4031" class="LineNr">4031 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[axx</span>
+<span id="L4032" class="LineNr">4032 </span><span class="Constant">bxx</span>
+<span id="L4033" class="LineNr">4033 </span><span class="Constant">cxx</span>
+<span id="L4034" class="LineNr">4034 </span><span class="Constant">dxx</span>
+<span id="L4035" class="LineNr">4035 </span><span class="Constant">exx</span>
+<span id="L4036" class="LineNr">4036 </span><span class="Constant">fxx</span>
+<span id="L4037" class="LineNr">4037 </span><span class="Constant">gxx</span>
+<span id="L4038" class="LineNr">4038 </span><span class="Constant">hxx</span>
+<span id="L4039" class="LineNr">4039 </span><span class="Constant">]</span>
+<span id="L4040" class="LineNr">4040 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L4041" class="LineNr">4041 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L4042" class="LineNr">4042 </span>  screen-should-contain [
+<span id="L4043" class="LineNr">4043 </span>   <span class="Constant"> .          .</span>
+<span id="L4044" class="LineNr">4044 </span>   <span class="Constant"> .axx       .</span>
+<span id="L4045" class="LineNr">4045 </span>   <span class="Constant"> .bxx       .</span>
+<span id="L4046" class="LineNr">4046 </span>   <span class="Constant"> .cxx       .</span>
+<span id="L4047" class="LineNr">4047 </span>  ]
+<span id="L4048" class="LineNr">4048 </span>  assume-console [
+<span id="L4049" class="LineNr">4049 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L4050" class="LineNr">4050 </span>  ]
+<span id="L4051" class="LineNr">4051 </span>  run [
+<span id="L4052" class="LineNr">4052 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4053" class="LineNr">4053 </span>  ]
+<span id="L4054" class="LineNr">4054 </span>  screen-should-contain [
+<span id="L4055" class="LineNr">4055 </span>   <span class="Constant"> .          .</span>
+<span id="L4056" class="LineNr">4056 </span>   <span class="Constant"> .cxx       .</span>
+<span id="L4057" class="LineNr">4057 </span>   <span class="Constant"> .dxx       .</span>
+<span id="L4058" class="LineNr">4058 </span>   <span class="Constant"> .exx       .</span>
+<span id="L4059" class="LineNr">4059 </span>  ]
 <span id="L4060" class="LineNr">4060 </span>  assume-console [
-<span id="L4061" class="LineNr">4061 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L4061" class="LineNr">4061 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L4062" class="LineNr">4062 </span>  ]
 <span id="L4063" class="LineNr">4063 </span>  run [
 <span id="L4064" class="LineNr">4064 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L4065" class="LineNr">4065 </span>  ]
 <span id="L4066" class="LineNr">4066 </span>  screen-should-contain [
 <span id="L4067" class="LineNr">4067 </span>   <span class="Constant"> .          .</span>
-<span id="L4068" class="LineNr">4068 </span>   <span class="Constant"> .cxx       .</span>
-<span id="L4069" class="LineNr">4069 </span>   <span class="Constant"> .dxx       .</span>
-<span id="L4070" class="LineNr">4070 </span>   <span class="Constant"> .exx       .</span>
+<span id="L4068" class="LineNr">4068 </span>   <span class="Constant"> .exx       .</span>
+<span id="L4069" class="LineNr">4069 </span>   <span class="Constant"> .fxx       .</span>
+<span id="L4070" class="LineNr">4070 </span>   <span class="Constant"> .gxx       .</span>
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-<span id="L4072" class="LineNr">4072 </span>]
-<span id="L4073" class="LineNr">4073 </span>
-<span id="L4074" class="LineNr">4074 </span><span class="muScenario">scenario</span> editor-can-scroll-up-past-empty-lines [
-<span id="L4075" class="LineNr">4075 </span>  <span class="Constant">local-scope</span>
-<span id="L4076" class="LineNr">4076 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
-<span id="L4077" class="LineNr">4077 </span>  <span class="Comment"># text with empty line in second screen</span>
-<span id="L4078" class="LineNr">4078 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[axy</span>
-<span id="L4079" class="LineNr">4079 </span><span class="Constant">bxy</span>
-<span id="L4080" class="LineNr">4080 </span><span class="Constant">cxy</span>
-<span id="L4081" class="LineNr">4081 </span>
-<span id="L4082" class="LineNr">4082 </span>dxy
-<span id="L4083" class="LineNr">4083 </span>exy
-<span id="L4084" class="LineNr">4084 </span>fxy
-<span id="L4085" class="LineNr">4085 </span>gxy
-<span id="L4086" class="LineNr">4086 </span>]
-<span id="L4087" class="LineNr">4087 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
-<span id="L4088" class="LineNr">4088 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
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-<span id="L4090" class="LineNr">4090 </span>   <span class="Constant"> .          .</span>
-<span id="L4091" class="LineNr">4091 </span>   <span class="Constant"> .axy       .</span>
-<span id="L4092" class="LineNr">4092 </span>   <span class="Constant"> .bxy       .</span>
-<span id="L4093" class="LineNr">4093 </span>   <span class="Constant"> .cxy       .</span>
-<span id="L4094" class="LineNr">4094 </span>  ]
-<span id="L4095" class="LineNr">4095 </span>  assume-console [
-<span id="L4096" class="LineNr">4096 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L4097" class="LineNr">4097 </span>  ]
-<span id="L4098" class="LineNr">4098 </span>  run [
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-<span id="L4100" class="LineNr">4100 </span>  ]
-<span id="L4101" class="LineNr">4101 </span>  screen-should-contain [
-<span id="L4102" class="LineNr">4102 </span>   <span class="Constant"> .          .</span>
-<span id="L4103" class="LineNr">4103 </span>   <span class="Constant"> .cxy       .</span>
-<span id="L4104" class="LineNr">4104 </span>   <span class="Constant"> .          .</span>
-<span id="L4105" class="LineNr">4105 </span>   <span class="Constant"> .dxy       .</span>
-<span id="L4106" class="LineNr">4106 </span>  ]
-<span id="L4107" class="LineNr">4107 </span>  assume-console [
-<span id="L4108" class="LineNr">4108 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L4109" class="LineNr">4109 </span>  ]
-<span id="L4110" class="LineNr">4110 </span>  run [
-<span id="L4111" class="LineNr">4111 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L4112" class="LineNr">4112 </span>  ]
-<span id="L4113" class="LineNr">4113 </span>  screen-should-contain [
-<span id="L4114" class="LineNr">4114 </span>   <span class="Constant"> .          .</span>
-<span id="L4115" class="LineNr">4115 </span>   <span class="Constant"> .dxy       .</span>
-<span id="L4116" class="LineNr">4116 </span>   <span class="Constant"> .exy       .</span>
-<span id="L4117" class="LineNr">4117 </span>   <span class="Constant"> .fxy       .</span>
-<span id="L4118" class="LineNr">4118 </span>  ]
-<span id="L4119" class="LineNr">4119 </span>  <span class="Comment"># scroll back up past empty line</span>
+<span id="L4072" class="LineNr">4072 </span>  <span class="Comment"># scroll back up past empty line</span>
+<span id="L4073" class="LineNr">4073 </span>  assume-console [
+<span id="L4074" class="LineNr">4074 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L4075" class="LineNr">4075 </span>  ]
+<span id="L4076" class="LineNr">4076 </span>  run [
+<span id="L4077" class="LineNr">4077 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4078" class="LineNr">4078 </span>  ]
+<span id="L4079" class="LineNr">4079 </span>  screen-should-contain [
+<span id="L4080" class="LineNr">4080 </span>   <span class="Constant"> .          .</span>
+<span id="L4081" class="LineNr">4081 </span>   <span class="Constant"> .cxx       .</span>
+<span id="L4082" class="LineNr">4082 </span>   <span class="Constant"> .dxx       .</span>
+<span id="L4083" class="LineNr">4083 </span>   <span class="Constant"> .exx       .</span>
+<span id="L4084" class="LineNr">4084 </span>  ]
+<span id="L4085" class="LineNr">4085 </span>]
+<span id="L4086" class="LineNr">4086 </span>
+<span id="L4087" class="LineNr">4087 </span><span class="muScenario">scenario</span> editor-can-scroll-up-past-empty-lines [
+<span id="L4088" class="LineNr">4088 </span>  <span class="Constant">local-scope</span>
+<span id="L4089" class="LineNr">4089 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">4/height</span>
+<span id="L4090" class="LineNr">4090 </span>  <span class="Comment"># text with empty line in second screen</span>
+<span id="L4091" class="LineNr">4091 </span>  s:text <span class="Special">&lt;-</span> new <span class="Constant">[axy</span>
+<span id="L4092" class="LineNr">4092 </span><span class="Constant">bxy</span>
+<span id="L4093" class="LineNr">4093 </span><span class="Constant">cxy</span>
+<span id="L4094" class="LineNr">4094 </span>
+<span id="L4095" class="LineNr">4095 </span>dxy
+<span id="L4096" class="LineNr">4096 </span>exy
+<span id="L4097" class="LineNr">4097 </span>fxy
+<span id="L4098" class="LineNr">4098 </span>gxy
+<span id="L4099" class="LineNr">4099 </span>]
+<span id="L4100" class="LineNr">4100 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> s, <span class="Constant">0/left</span>, <span class="Constant">4/right</span>
+<span id="L4101" class="LineNr">4101 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L4102" class="LineNr">4102 </span>  screen-should-contain [
+<span id="L4103" class="LineNr">4103 </span>   <span class="Constant"> .          .</span>
+<span id="L4104" class="LineNr">4104 </span>   <span class="Constant"> .axy       .</span>
+<span id="L4105" class="LineNr">4105 </span>   <span class="Constant"> .bxy       .</span>
+<span id="L4106" class="LineNr">4106 </span>   <span class="Constant"> .cxy       .</span>
+<span id="L4107" class="LineNr">4107 </span>  ]
+<span id="L4108" class="LineNr">4108 </span>  assume-console [
+<span id="L4109" class="LineNr">4109 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L4110" class="LineNr">4110 </span>  ]
+<span id="L4111" class="LineNr">4111 </span>  run [
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+<span id="L4113" class="LineNr">4113 </span>  ]
+<span id="L4114" class="LineNr">4114 </span>  screen-should-contain [
+<span id="L4115" class="LineNr">4115 </span>   <span class="Constant"> .          .</span>
+<span id="L4116" class="LineNr">4116 </span>   <span class="Constant"> .cxy       .</span>
+<span id="L4117" class="LineNr">4117 </span>   <span class="Constant"> .          .</span>
+<span id="L4118" class="LineNr">4118 </span>   <span class="Constant"> .dxy       .</span>
+<span id="L4119" class="LineNr">4119 </span>  ]
 <span id="L4120" class="LineNr">4120 </span>  assume-console [
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+<span id="L4121" class="LineNr">4121 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L4122" class="LineNr">4122 </span>  ]
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 <span id="L4124" class="LineNr">4124 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L4125" class="LineNr">4125 </span>  ]
 <span id="L4126" class="LineNr">4126 </span>  screen-should-contain [
 <span id="L4127" class="LineNr">4127 </span>   <span class="Constant"> .          .</span>
-<span id="L4128" class="LineNr">4128 </span>   <span class="Constant"> .cxy       .</span>
-<span id="L4129" class="LineNr">4129 </span>   <span class="Constant"> .          .</span>
-<span id="L4130" class="LineNr">4130 </span>   <span class="Constant"> .dxy       .</span>
+<span id="L4128" class="LineNr">4128 </span>   <span class="Constant"> .dxy       .</span>
+<span id="L4129" class="LineNr">4129 </span>   <span class="Constant"> .exy       .</span>
+<span id="L4130" class="LineNr">4130 </span>   <span class="Constant"> .fxy       .</span>
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-<span id="L4133" class="LineNr">4133 </span>
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-<span id="L4136" class="LineNr">4136 </span>
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-<span id="L4140" class="LineNr">4140 </span>    <span class="muControl">break-unless</span> scroll-up?
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-<span id="L4142" class="LineNr">4142 </span>    go-render?:bool, editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4149'>line-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L4143" class="LineNr">4143 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">5/line-up</span>
-<span id="L4144" class="LineNr">4144 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L4145" class="LineNr">4145 </span>   <span class="muControl"> return</span> go-render?
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-<span id="L4148" class="LineNr">4148 </span>
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-<span id="L4151" class="LineNr">4151 </span>  <span class="Constant">load-inputs</span>
-<span id="L4152" class="LineNr">4152 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
-<span id="L4153" class="LineNr">4153 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
-<span id="L4154" class="LineNr">4154 </span>  max:num <span class="Special">&lt;-</span> subtract right, left
-<span id="L4155" class="LineNr">4155 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L4156" class="LineNr">4156 </span>  new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L2849'>before-start-of-next-line</a> old-top, max
-<span id="L4157" class="LineNr">4157 </span>  movement?:bool <span class="Special">&lt;-</span> not-equal old-top, new-top
-<span id="L4158" class="LineNr">4158 </span>  <span class="Delimiter">{</span>
-<span id="L4159" class="LineNr">4159 </span>    <span class="muControl">break-unless</span> movement?
-<span id="L4160" class="LineNr">4160 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
-<span id="L4161" class="LineNr">4161 </span>  <span class="Delimiter">}</span>
-<span id="L4162" class="LineNr">4162 </span> <span class="muControl"> return</span> movement?
-<span id="L4163" class="LineNr">4163 </span>]
-<span id="L4164" class="LineNr">4164 </span>
-<span id="L4165" class="LineNr">4165 </span><span class="Comment"># ctrl-x - scroll down by one line</span>
-<span id="L4166" class="LineNr">4166 </span><span class="Comment"># todo: scenarios</span>
-<span id="L4167" class="LineNr">4167 </span>
-<span id="L4168" class="LineNr">4168 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
-<span id="L4169" class="LineNr">4169 </span>  <span class="Delimiter">{</span>
-<span id="L4170" class="LineNr">4170 </span>    scroll-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">24/ctrl-x</span>
-<span id="L4171" class="LineNr">4171 </span>    <span class="muControl">break-unless</span> scroll-down?
-<span id="L4172" class="LineNr">4172 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L4173" class="LineNr">4173 </span>    go-render?:bool, editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4180'>line-down</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
-<span id="L4174" class="LineNr">4174 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">6/line-down</span>
-<span id="L4175" class="LineNr">4175 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L4176" class="LineNr">4176 </span>   <span class="muControl"> return</span> go-render?
-<span id="L4177" class="LineNr">4177 </span>  <span class="Delimiter">}</span>
-<span id="L4178" class="LineNr">4178 </span>]
-<span id="L4179" class="LineNr">4179 </span>
-<span id="L4180" class="LineNr">4180 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4180'>line-down</a> editor:&amp;:editor, <a href='../081print.mu.html#L782'>screen-height</a>:num<span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor [
-<span id="L4181" class="LineNr">4181 </span>  <span class="Constant">local-scope</span>
-<span id="L4182" class="LineNr">4182 </span>  <span class="Constant">load-inputs</span>
-<span id="L4183" class="LineNr">4183 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L4184" class="LineNr">4184 </span>  new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> old-top, editor
-<span id="L4185" class="LineNr">4185 </span>  movement?:bool <span class="Special">&lt;-</span> not-equal old-top, new-top
-<span id="L4186" class="LineNr">4186 </span>  <span class="Delimiter">{</span>
-<span id="L4187" class="LineNr">4187 </span>    <span class="muControl">break-unless</span> movement?
-<span id="L4188" class="LineNr">4188 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
-<span id="L4189" class="LineNr">4189 </span>  <span class="Delimiter">}</span>
-<span id="L4190" class="LineNr">4190 </span> <span class="muControl"> return</span> movement?
+<span id="L4132" class="LineNr">4132 </span>  <span class="Comment"># scroll back up past empty line</span>
+<span id="L4133" class="LineNr">4133 </span>  assume-console [
+<span id="L4134" class="LineNr">4134 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
+<span id="L4135" class="LineNr">4135 </span>  ]
+<span id="L4136" class="LineNr">4136 </span>  run [
+<span id="L4137" class="LineNr">4137 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4138" class="LineNr">4138 </span>  ]
+<span id="L4139" class="LineNr">4139 </span>  screen-should-contain [
+<span id="L4140" class="LineNr">4140 </span>   <span class="Constant"> .          .</span>
+<span id="L4141" class="LineNr">4141 </span>   <span class="Constant"> .cxy       .</span>
+<span id="L4142" class="LineNr">4142 </span>   <span class="Constant"> .          .</span>
+<span id="L4143" class="LineNr">4143 </span>   <span class="Constant"> .dxy       .</span>
+<span id="L4144" class="LineNr">4144 </span>  ]
+<span id="L4145" class="LineNr">4145 </span>]
+<span id="L4146" class="LineNr">4146 </span>
+<span id="L4147" class="LineNr">4147 </span><span class="Comment"># ctrl-s - scroll up by one line</span>
+<span id="L4148" class="LineNr">4148 </span><span class="Comment"># todo: scenarios</span>
+<span id="L4149" class="LineNr">4149 </span>
+<span id="L4150" class="LineNr">4150 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L4151" class="LineNr">4151 </span>  <span class="Delimiter">{</span>
+<span id="L4152" class="LineNr">4152 </span>    scroll-up?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">19/ctrl-s</span>
+<span id="L4153" class="LineNr">4153 </span>    <span class="muControl">break-unless</span> scroll-up?
+<span id="L4154" class="LineNr">4154 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L4155" class="LineNr">4155 </span>    go-render?:bool, editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4162'>line-up</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L4156" class="LineNr">4156 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">5/line-up</span>
+<span id="L4157" class="LineNr">4157 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L4158" class="LineNr">4158 </span>   <span class="muControl"> return</span> go-render?
+<span id="L4159" class="LineNr">4159 </span>  <span class="Delimiter">}</span>
+<span id="L4160" class="LineNr">4160 </span>]
+<span id="L4161" class="LineNr">4161 </span>
+<span id="L4162" class="LineNr">4162 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4162'>line-up</a> editor:&amp;:editor, <a href='../081print.mu.html#L782'>screen-height</a>:num<span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor [
+<span id="L4163" class="LineNr">4163 </span>  <span class="Constant">local-scope</span>
+<span id="L4164" class="LineNr">4164 </span>  <span class="Constant">load-inputs</span>
+<span id="L4165" class="LineNr">4165 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
+<span id="L4166" class="LineNr">4166 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
+<span id="L4167" class="LineNr">4167 </span>  max:num <span class="Special">&lt;-</span> subtract right, left
+<span id="L4168" class="LineNr">4168 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L4169" class="LineNr">4169 </span>  new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L2862'>before-start-of-next-line</a> old-top, max
+<span id="L4170" class="LineNr">4170 </span>  movement?:bool <span class="Special">&lt;-</span> not-equal old-top, new-top
+<span id="L4171" class="LineNr">4171 </span>  <span class="Delimiter">{</span>
+<span id="L4172" class="LineNr">4172 </span>    <span class="muControl">break-unless</span> movement?
+<span id="L4173" class="LineNr">4173 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
+<span id="L4174" class="LineNr">4174 </span>  <span class="Delimiter">}</span>
+<span id="L4175" class="LineNr">4175 </span> <span class="muControl"> return</span> movement?
+<span id="L4176" class="LineNr">4176 </span>]
+<span id="L4177" class="LineNr">4177 </span>
+<span id="L4178" class="LineNr">4178 </span><span class="Comment"># ctrl-x - scroll down by one line</span>
+<span id="L4179" class="LineNr">4179 </span><span class="Comment"># todo: scenarios</span>
+<span id="L4180" class="LineNr">4180 </span>
+<span id="L4181" class="LineNr">4181 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L4182" class="LineNr">4182 </span>  <span class="Delimiter">{</span>
+<span id="L4183" class="LineNr">4183 </span>    scroll-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">24/ctrl-x</span>
+<span id="L4184" class="LineNr">4184 </span>    <span class="muControl">break-unless</span> scroll-down?
+<span id="L4185" class="LineNr">4185 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L4186" class="LineNr">4186 </span>    go-render?:bool, editor <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4193'>line-down</a> editor, <a href='../081print.mu.html#L782'>screen-height</a>
+<span id="L4187" class="LineNr">4187 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">6/line-down</span>
+<span id="L4188" class="LineNr">4188 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L4189" class="LineNr">4189 </span>   <span class="muControl"> return</span> go-render?
+<span id="L4190" class="LineNr">4190 </span>  <span class="Delimiter">}</span>
 <span id="L4191" class="LineNr">4191 </span>]
 <span id="L4192" class="LineNr">4192 </span>
-<span id="L4193" class="LineNr">4193 </span><span class="Comment"># ctrl-t - move current line to top of screen</span>
-<span id="L4194" class="LineNr">4194 </span><span class="Comment"># todo: scenarios</span>
-<span id="L4195" class="LineNr">4195 </span>
-<span id="L4196" class="LineNr">4196 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
-<span id="L4197" class="LineNr">4197 </span>  <span class="Delimiter">{</span>
-<span id="L4198" class="LineNr">4198 </span>    scroll-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">20/ctrl-t</span>
-<span id="L4199" class="LineNr">4199 </span>    <span class="muControl">break-unless</span> scroll-down?
-<span id="L4200" class="LineNr">4200 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
-<span id="L4201" class="LineNr">4201 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L4202" class="LineNr">4202 </span>    cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L4203" class="LineNr">4203 </span>    cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> cursor
-<span id="L4204" class="LineNr">4204 </span>    new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> cursor, editor
-<span id="L4205" class="LineNr">4205 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
-<span id="L4206" class="LineNr">4206 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>,<span class="Constant"> 1</span>
-<span id="L4207" class="LineNr">4207 </span>    go-render?:bool <span class="Special">&lt;-</span> not-equal new-top, old-top
-<span id="L4208" class="LineNr">4208 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
-<span id="L4209" class="LineNr">4209 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
-<span id="L4210" class="LineNr">4210 </span>   <span class="muControl"> return</span> go-render?
-<span id="L4211" class="LineNr">4211 </span>  <span class="Delimiter">}</span>
-<span id="L4212" class="LineNr">4212 </span>]
-<span id="L4213" class="LineNr">4213 </span>
-<span id="L4214" class="LineNr">4214 </span><span class="Comment"># ctrl-/ - comment/uncomment current line</span>
-<span id="L4215" class="LineNr">4215 </span>
-<span id="L4216" class="LineNr">4216 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
-<span id="L4217" class="LineNr">4217 </span>  <span class="Delimiter">{</span>
-<span id="L4218" class="LineNr">4218 </span>    comment-toggle?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">31/ctrl-slash</span>
-<span id="L4219" class="LineNr">4219 </span>    <span class="muControl">break-unless</span> comment-toggle?
-<span id="L4220" class="LineNr">4220 </span>    cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
-<span id="L4221" class="LineNr">4221 </span>    data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L4222" class="LineNr">4222 </span><span class="Constant">    &lt;begin-insert-character&gt;</span>
-<span id="L4223" class="LineNr">4223 </span>    before-line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4280'>before-start-of-screen-line</a> editor
-<span id="L4224" class="LineNr">4224 </span>    line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-line-start
-<span id="L4225" class="LineNr">4225 </span>    commented-out?:bool <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L585'>match</a> line-start, <span class="Constant">[#? ]</span>  <span class="Comment"># comment prefix</span>
-<span id="L4226" class="LineNr">4226 </span>    <span class="Delimiter">{</span>
-<span id="L4227" class="LineNr">4227 </span>      <span class="muControl">break-unless</span> commented-out?
-<span id="L4228" class="LineNr">4228 </span>      <span class="Comment"># uncomment</span>
-<span id="L4229" class="LineNr">4229 </span>      data <span class="Special">&lt;-</span> remove line-start, <span class="Constant">3/length-comment-prefix</span>, data
-<span id="L4230" class="LineNr">4230 </span>      cursor-column <span class="Special">&lt;-</span> subtract cursor-column, <span class="Constant">3/length-comment-prefix</span>
-<span id="L4231" class="LineNr">4231 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L4232" class="LineNr">4232 </span>      go-render? <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4250'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>, editor, <span class="Constant">3/size-of-comment-leader</span>
-<span id="L4233" class="LineNr">4233 </span>    <span class="Delimiter">}</span>
-<span id="L4234" class="LineNr">4234 </span>    <span class="Delimiter">{</span>
-<span id="L4235" class="LineNr">4235 </span>      <span class="muControl">break-if</span> commented-out?
-<span id="L4236" class="LineNr">4236 </span>      <span class="Comment"># comment</span>
-<span id="L4237" class="LineNr">4237 </span>      insert before-line-start, <span class="Constant">[#? ]</span>
-<span id="L4238" class="LineNr">4238 </span>      cursor-column <span class="Special">&lt;-</span> add cursor-column, <span class="Constant">3/length-comment-prefix</span>
-<span id="L4239" class="LineNr">4239 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
-<span id="L4240" class="LineNr">4240 </span>      go-render? <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4250'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>, editor,<span class="Constant"> 0</span>
-<span id="L4241" class="LineNr">4241 </span>    <span class="Delimiter">}</span>
-<span id="L4242" class="LineNr">4242 </span><span class="Constant">    &lt;end-insert-character&gt;</span>
-<span id="L4243" class="LineNr">4243 </span>   <span class="muControl"> return</span>
-<span id="L4244" class="LineNr">4244 </span>  <span class="Delimiter">}</span>
-<span id="L4245" class="LineNr">4245 </span>]
-<span id="L4246" class="LineNr">4246 </span>
-<span id="L4247" class="LineNr">4247 </span><span class="Comment"># Render just from the start of the current line, and only if it wasn't</span>
-<span id="L4248" class="LineNr">4248 </span><span class="Comment"># wrapping before (include margin) and isn't wrapping now. Otherwise just tell</span>
-<span id="L4249" class="LineNr">4249 </span><span class="Comment"># the caller to go-render? the entire screen.</span>
-<span id="L4250" class="LineNr">4250 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4250'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor, right-margin:num<span class="muRecipe"> -&gt; </span>go-render?:bool, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
-<span id="L4251" class="LineNr">4251 </span>  <span class="Constant">local-scope</span>
-<span id="L4252" class="LineNr">4252 </span>  <span class="Constant">load-inputs</span>
-<span id="L4253" class="LineNr">4253 </span>  before-line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4280'>before-start-of-screen-line</a> editor
-<span id="L4254" class="LineNr">4254 </span>  line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-line-start
-<span id="L4255" class="LineNr">4255 </span>  color:num <span class="Special">&lt;-</span> copy <span class="Constant">7/white</span>
-<span id="L4256" class="LineNr">4256 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
-<span id="L4257" class="LineNr">4257 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
-<span id="L4258" class="LineNr">4258 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, cursor-row, left
-<span id="L4259" class="LineNr">4259 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
-<span id="L4260" class="LineNr">4260 </span>  end:num <span class="Special">&lt;-</span> subtract right, right-margin
-<span id="L4261" class="LineNr">4261 </span>  i:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
-<span id="L4262" class="LineNr">4262 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy line-start
-<span id="L4263" class="LineNr">4263 </span>  <span class="Delimiter">{</span>
-<span id="L4264" class="LineNr">4264 </span>    render-all?:bool <span class="Special">&lt;-</span> greater-or-equal i, end
-<span id="L4265" class="LineNr">4265 </span>    <span class="muControl">return-if</span> render-all?, <span class="Constant">1/go-render</span>
-<span id="L4266" class="LineNr">4266 </span>    <span class="muControl">break-unless</span> curr
-<span id="L4267" class="LineNr">4267 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
-<span id="L4268" class="LineNr">4268 </span>    newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
-<span id="L4269" class="LineNr">4269 </span>    <span class="muControl">break-if</span> newline?
-<span id="L4270" class="LineNr">4270 </span>    color <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L398'>get-color</a> color, c
-<span id="L4271" class="LineNr">4271 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c, color
-<span id="L4272" class="LineNr">4272 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L4273" class="LineNr">4273 </span>    i <span class="Special">&lt;-</span> add i,<span class="Constant"> 1</span>
-<span id="L4274" class="LineNr">4274 </span>   <span class="muControl"> loop</span>
-<span id="L4275" class="LineNr">4275 </span>  <span class="Delimiter">}</span>
-<span id="L4276" class="LineNr">4276 </span>  <a href='../081print.mu.html#L553'>clear-line-until</a> <a href='../081print.mu.html#L16'>screen</a>, right
-<span id="L4277" class="LineNr">4277 </span> <span class="muControl"> return</span> <span class="Constant">0/dont-render</span>
-<span id="L4278" class="LineNr">4278 </span>]
-<span id="L4279" class="LineNr">4279 </span>
-<span id="L4280" class="LineNr">4280 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4280'>before-start-of-screen-line</a> editor:&amp;:editor<span class="muRecipe"> -&gt; </span>result:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char [
-<span id="L4281" class="LineNr">4281 </span>  <span class="Constant">local-scope</span>
-<span id="L4282" class="LineNr">4282 </span>  <span class="Constant">load-inputs</span>
-<span id="L4283" class="LineNr">4283 </span>  cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L4284" class="LineNr">4284 </span>  <span class="Delimiter">{</span>
-<span id="L4285" class="LineNr">4285 </span>    <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> cursor
-<span id="L4286" class="LineNr">4286 </span>    <span class="muControl">break-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>
-<span id="L4287" class="LineNr">4287 </span>    cursor <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L25'>next</a>
+<span id="L4193" class="LineNr">4193 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4193'>line-down</a> editor:&amp;:editor, <a href='../081print.mu.html#L782'>screen-height</a>:num<span class="muRecipe"> -&gt; </span>go-render?:bool, editor:&amp;:editor [
+<span id="L4194" class="LineNr">4194 </span>  <span class="Constant">local-scope</span>
+<span id="L4195" class="LineNr">4195 </span>  <span class="Constant">load-inputs</span>
+<span id="L4196" class="LineNr">4196 </span>  old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L4197" class="LineNr">4197 </span>  new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> old-top, editor
+<span id="L4198" class="LineNr">4198 </span>  movement?:bool <span class="Special">&lt;-</span> not-equal old-top, new-top
+<span id="L4199" class="LineNr">4199 </span>  <span class="Delimiter">{</span>
+<span id="L4200" class="LineNr">4200 </span>    <span class="muControl">break-unless</span> movement?
+<span id="L4201" class="LineNr">4201 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
+<span id="L4202" class="LineNr">4202 </span>  <span class="Delimiter">}</span>
+<span id="L4203" class="LineNr">4203 </span> <span class="muControl"> return</span> movement?
+<span id="L4204" class="LineNr">4204 </span>]
+<span id="L4205" class="LineNr">4205 </span>
+<span id="L4206" class="LineNr">4206 </span><span class="Comment"># ctrl-t - move current line to top of screen</span>
+<span id="L4207" class="LineNr">4207 </span><span class="Comment"># todo: scenarios</span>
+<span id="L4208" class="LineNr">4208 </span>
+<span id="L4209" class="LineNr">4209 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L4210" class="LineNr">4210 </span>  <span class="Delimiter">{</span>
+<span id="L4211" class="LineNr">4211 </span>    scroll-down?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">20/ctrl-t</span>
+<span id="L4212" class="LineNr">4212 </span>    <span class="muControl">break-unless</span> scroll-down?
+<span id="L4213" class="LineNr">4213 </span><span class="Constant">    &lt;begin-move-cursor&gt;</span>
+<span id="L4214" class="LineNr">4214 </span>    old-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
+<span id="L4215" class="LineNr">4215 </span>    cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
+<span id="L4216" class="LineNr">4216 </span>    cursor <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> cursor
+<span id="L4217" class="LineNr">4217 </span>    new-top:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> cursor, editor
+<span id="L4218" class="LineNr">4218 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">top-of-screen:offset</span>, new-top
+<span id="L4219" class="LineNr">4219 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>,<span class="Constant"> 1</span>
+<span id="L4220" class="LineNr">4220 </span>    go-render?:bool <span class="Special">&lt;-</span> not-equal new-top, old-top
+<span id="L4221" class="LineNr">4221 </span>    undo-coalesce-tag:num <span class="Special">&lt;-</span> copy <span class="Constant">0/never</span>
+<span id="L4222" class="LineNr">4222 </span><span class="Constant">    &lt;end-move-cursor&gt;</span>
+<span id="L4223" class="LineNr">4223 </span>   <span class="muControl"> return</span> go-render?
+<span id="L4224" class="LineNr">4224 </span>  <span class="Delimiter">}</span>
+<span id="L4225" class="LineNr">4225 </span>]
+<span id="L4226" class="LineNr">4226 </span>
+<span id="L4227" class="LineNr">4227 </span><span class="Comment"># ctrl-/ - comment/uncomment current line</span>
+<span id="L4228" class="LineNr">4228 </span>
+<span id="L4229" class="LineNr">4229 </span><span class="muRecipe">after</span> <span class="Constant"><a href='002-typing.mu.html#L185'>&lt;handle-special-character&gt;</a></span> [
+<span id="L4230" class="LineNr">4230 </span>  <span class="Delimiter">{</span>
+<span id="L4231" class="LineNr">4231 </span>    comment-toggle?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">31/ctrl-slash</span>
+<span id="L4232" class="LineNr">4232 </span>    <span class="muControl">break-unless</span> comment-toggle?
+<span id="L4233" class="LineNr">4233 </span>    cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
+<span id="L4234" class="LineNr">4234 </span>    data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
+<span id="L4235" class="LineNr">4235 </span><span class="Constant">    &lt;begin-insert-character&gt;</span>
+<span id="L4236" class="LineNr">4236 </span>    before-line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4293'>before-start-of-screen-line</a> editor
+<span id="L4237" class="LineNr">4237 </span>    line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-line-start
+<span id="L4238" class="LineNr">4238 </span>    commented-out?:bool <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L642'>match</a> line-start, <span class="Constant">[#? ]</span>  <span class="Comment"># comment prefix</span>
+<span id="L4239" class="LineNr">4239 </span>    <span class="Delimiter">{</span>
+<span id="L4240" class="LineNr">4240 </span>      <span class="muControl">break-unless</span> commented-out?
+<span id="L4241" class="LineNr">4241 </span>      <span class="Comment"># uncomment</span>
+<span id="L4242" class="LineNr">4242 </span>      data <span class="Special">&lt;-</span> remove line-start, <span class="Constant">3/length-comment-prefix</span>, data
+<span id="L4243" class="LineNr">4243 </span>      cursor-column <span class="Special">&lt;-</span> subtract cursor-column, <span class="Constant">3/length-comment-prefix</span>
+<span id="L4244" class="LineNr">4244 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
+<span id="L4245" class="LineNr">4245 </span>      go-render? <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4263'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>, editor, <span class="Constant">3/size-of-comment-leader</span>
+<span id="L4246" class="LineNr">4246 </span>    <span class="Delimiter">}</span>
+<span id="L4247" class="LineNr">4247 </span>    <span class="Delimiter">{</span>
+<span id="L4248" class="LineNr">4248 </span>      <span class="muControl">break-if</span> commented-out?
+<span id="L4249" class="LineNr">4249 </span>      <span class="Comment"># comment</span>
+<span id="L4250" class="LineNr">4250 </span>      insert before-line-start, <span class="Constant">[#? ]</span>
+<span id="L4251" class="LineNr">4251 </span>      cursor-column <span class="Special">&lt;-</span> add cursor-column, <span class="Constant">3/length-comment-prefix</span>
+<span id="L4252" class="LineNr">4252 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, cursor-column
+<span id="L4253" class="LineNr">4253 </span>      go-render? <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4263'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>, editor,<span class="Constant"> 0</span>
+<span id="L4254" class="LineNr">4254 </span>    <span class="Delimiter">}</span>
+<span id="L4255" class="LineNr">4255 </span><span class="Constant">    &lt;end-insert-character&gt;</span>
+<span id="L4256" class="LineNr">4256 </span>   <span class="muControl"> return</span>
+<span id="L4257" class="LineNr">4257 </span>  <span class="Delimiter">}</span>
+<span id="L4258" class="LineNr">4258 </span>]
+<span id="L4259" class="LineNr">4259 </span>
+<span id="L4260" class="LineNr">4260 </span><span class="Comment"># Render just from the start of the current line, and only if it wasn't</span>
+<span id="L4261" class="LineNr">4261 </span><span class="Comment"># wrapping before (include margin) and isn't wrapping now. Otherwise just tell</span>
+<span id="L4262" class="LineNr">4262 </span><span class="Comment"># the caller to go-render? the entire screen.</span>
+<span id="L4263" class="LineNr">4263 </span><span class="muRecipe">def</span> <a href='003-shortcuts.mu.html#L4263'>render-line-from-start</a> <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a>, editor:&amp;:editor, right-margin:num<span class="muRecipe"> -&gt; </span>go-render?:bool, <a href='../081print.mu.html#L16'>screen</a>:&amp;:<a href='../081print.mu.html#L16'>screen</a> [
+<span id="L4264" class="LineNr">4264 </span>  <span class="Constant">local-scope</span>
+<span id="L4265" class="LineNr">4265 </span>  <span class="Constant">load-inputs</span>
+<span id="L4266" class="LineNr">4266 </span>  before-line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L4293'>before-start-of-screen-line</a> editor
+<span id="L4267" class="LineNr">4267 </span>  line-start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-line-start
+<span id="L4268" class="LineNr">4268 </span>  color:num <span class="Special">&lt;-</span> copy <span class="Constant">7/white</span>
+<span id="L4269" class="LineNr">4269 </span>  left:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">left:offset</span>
+<span id="L4270" class="LineNr">4270 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
+<span id="L4271" class="LineNr">4271 </span>  <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, cursor-row, left
+<span id="L4272" class="LineNr">4272 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
+<span id="L4273" class="LineNr">4273 </span>  end:num <span class="Special">&lt;-</span> subtract right, right-margin
+<span id="L4274" class="LineNr">4274 </span>  i:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
+<span id="L4275" class="LineNr">4275 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy line-start
+<span id="L4276" class="LineNr">4276 </span>  <span class="Delimiter">{</span>
+<span id="L4277" class="LineNr">4277 </span>    render-all?:bool <span class="Special">&lt;-</span> greater-or-equal i, end
+<span id="L4278" class="LineNr">4278 </span>    <span class="muControl">return-if</span> render-all?,<span class="Constant"> true/go-render</span>
+<span id="L4279" class="LineNr">4279 </span>    <span class="muControl">break-unless</span> curr
+<span id="L4280" class="LineNr">4280 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
+<span id="L4281" class="LineNr">4281 </span>    newline?:bool <span class="Special">&lt;-</span> equal c, <span class="Constant">10/newline</span>
+<span id="L4282" class="LineNr">4282 </span>    <span class="muControl">break-if</span> newline?
+<span id="L4283" class="LineNr">4283 </span>    color <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L400'>get-color</a> color, c
+<span id="L4284" class="LineNr">4284 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c, color
+<span id="L4285" class="LineNr">4285 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L4286" class="LineNr">4286 </span>    i <span class="Special">&lt;-</span> add i,<span class="Constant"> 1</span>
+<span id="L4287" class="LineNr">4287 </span>   <span class="muControl"> loop</span>
 <span id="L4288" class="LineNr">4288 </span>  <span class="Delimiter">}</span>
-<span id="L4289" class="LineNr">4289 </span>  result <span class="Special">&lt;-</span> <a href='003-shortcuts.mu.html#L1067'>before-previous-screen-line</a> cursor, editor
-<span id="L4290" class="LineNr">4290 </span>]
-<span id="L4291" class="LineNr">4291 </span>
-<span id="L4292" class="LineNr">4292 </span><span class="muScenario">scenario</span> editor-comments-empty-line [
-<span id="L4293" class="LineNr">4293 </span>  <span class="Constant">local-scope</span>
-<span id="L4294" class="LineNr">4294 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
-<span id="L4295" class="LineNr">4295 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
-<span id="L4296" class="LineNr">4296 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L4297" class="LineNr">4297 </span>  $clear-trace
-<span id="L4298" class="LineNr">4298 </span>  assume-console [
-<span id="L4299" class="LineNr">4299 </span>    press ctrl-slash
-<span id="L4300" class="LineNr">4300 </span>  ]
-<span id="L4301" class="LineNr">4301 </span>  run [
-<span id="L4302" class="LineNr">4302 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L4303" class="LineNr">4303 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L4304" class="LineNr">4304 </span>    5:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
-<span id="L4305" class="LineNr">4305 </span>  ]
-<span id="L4306" class="LineNr">4306 </span>  screen-should-contain [
-<span id="L4307" class="LineNr">4307 </span>   <span class="Constant"> .          .</span>
-<span id="L4308" class="LineNr">4308 </span>   <span class="Constant"> .#?        .</span>
-<span id="L4309" class="LineNr">4309 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
-<span id="L4310" class="LineNr">4310 </span>   <span class="Constant"> .          .</span>
-<span id="L4311" class="LineNr">4311 </span>  ]
-<span id="L4312" class="LineNr">4312 </span>  memory-should-contain [
-<span id="L4313" class="LineNr">4313 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
-<span id="L4314" class="LineNr">4314 </span>   <span class="Constant"> 5</span> <span class="Special">&lt;-</span><span class="Constant"> 3</span>
-<span id="L4315" class="LineNr">4315 </span>  ]
-<span id="L4316" class="LineNr">4316 </span>  check-trace-count-for-label<span class="Constant"> 5</span>, <span class="Constant">[print-character]</span>
-<span id="L4317" class="LineNr">4317 </span>]
-<span id="L4318" class="LineNr">4318 </span>
-<span id="L4319" class="LineNr">4319 </span><span class="muScenario">scenario</span> editor-comments-at-start-of-contents [
-<span id="L4320" class="LineNr">4320 </span>  <span class="Constant">local-scope</span>
-<span id="L4321" class="LineNr">4321 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
-<span id="L4322" class="LineNr">4322 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[ab]</span>, <span class="Constant">0/left</span>, <span class="Constant">10/right</span>
-<span id="L4323" class="LineNr">4323 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
-<span id="L4324" class="LineNr">4324 </span>  $clear-trace
-<span id="L4325" class="LineNr">4325 </span>  assume-console [
-<span id="L4326" class="LineNr">4326 </span>    press ctrl-slash
-<span id="L4327" class="LineNr">4327 </span>  ]
-<span id="L4328" class="LineNr">4328 </span>  run [
-<span id="L4329" class="LineNr">4329 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
-<span id="L4330" class="LineNr">4330 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
-<span id="L4331" class="LineNr">4331 </span>    5:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
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+<span id="L4369" class="LineNr">4369 </span>  run [
+<span id="L4370" class="LineNr">4370 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4371" class="LineNr">4371 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L4372" class="LineNr">4372 </span>    5:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L4373" class="LineNr">4373 </span>  ]
+<span id="L4374" class="LineNr">4374 </span>  screen-should-contain [
+<span id="L4375" class="LineNr">4375 </span>   <span class="Constant"> .          .</span>
+<span id="L4376" class="LineNr">4376 </span>   <span class="Constant"> .#? ab     .</span>
+<span id="L4377" class="LineNr">4377 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L4378" class="LineNr">4378 </span>   <span class="Constant"> .          .</span>
+<span id="L4379" class="LineNr">4379 </span>  ]
+<span id="L4380" class="LineNr">4380 </span>  memory-should-contain [
+<span id="L4381" class="LineNr">4381 </span>   <span class="Constant"> 4</span> <span class="Special">&lt;-</span><span class="Constant"> 1</span>
+<span id="L4382" class="LineNr">4382 </span>   <span class="Constant"> 5</span> <span class="Special">&lt;-</span><span class="Constant"> 5</span>
+<span id="L4383" class="LineNr">4383 </span>  ]
+<span id="L4384" class="LineNr">4384 </span>  check-trace-count-for-label<span class="Constant"> 10</span>, <span class="Constant">[print-character]</span>
+<span id="L4385" class="LineNr">4385 </span>  <span class="Comment"># toggle to uncomment</span>
+<span id="L4386" class="LineNr">4386 </span>  $clear-trace
+<span id="L4387" class="LineNr">4387 </span>  assume-console [
+<span id="L4388" class="LineNr">4388 </span>    press ctrl-slash
+<span id="L4389" class="LineNr">4389 </span>  ]
+<span id="L4390" class="LineNr">4390 </span>  run [
+<span id="L4391" class="LineNr">4391 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4392" class="LineNr">4392 </span>    4:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-row:offset</span>
+<span id="L4393" class="LineNr">4393 </span>    5:num/<span class="Special">raw</span> <span class="Special">&lt;-</span> get *e, <span class="Constant">cursor-column:offset</span>
+<span id="L4394" class="LineNr">4394 </span>  ]
+<span id="L4395" class="LineNr">4395 </span>  screen-should-contain [
+<span id="L4396" class="LineNr">4396 </span>   <span class="Constant"> .          .</span>
+<span id="L4397" class="LineNr">4397 </span>   <span class="Constant"> .ab        .</span>
+<span id="L4398" class="LineNr">4398 </span><span class="Constant">    .╌╌╌╌╌╌╌╌╌╌.</span>
+<span id="L4399" class="LineNr">4399 </span>   <span class="Constant"> .          .</span>
+<span id="L4400" class="LineNr">4400 </span>  ]
+<span id="L4401" class="LineNr">4401 </span>  check-trace-count-for-label<span class="Constant"> 10</span>, <span class="Constant">[print-character]</span>
+<span id="L4402" class="LineNr">4402 </span>]
+<span id="L4403" class="LineNr">4403 </span>
+<span id="L4404" class="LineNr">4404 </span><span class="muScenario">scenario</span> editor-comments-almost-wrapping-line [
+<span id="L4405" class="LineNr">4405 </span>  <span class="Constant">local-scope</span>
+<span id="L4406" class="LineNr">4406 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
+<span id="L4407" class="LineNr">4407 </span>  <span class="Comment"># editor starts out with a non-wrapping line</span>
+<span id="L4408" class="LineNr">4408 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[abcd]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L4409" class="LineNr">4409 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L4410" class="LineNr">4410 </span>  screen-should-contain [
+<span id="L4411" class="LineNr">4411 </span>   <span class="Constant"> .          .</span>
+<span id="L4412" class="LineNr">4412 </span>   <span class="Constant"> .abcd      .</span>
+<span id="L4413" class="LineNr">4413 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
+<span id="L4414" class="LineNr">4414 </span>   <span class="Constant"> .          .</span>
+<span id="L4415" class="LineNr">4415 </span>  ]
+<span id="L4416" class="LineNr">4416 </span>  $clear-trace
+<span id="L4417" class="LineNr">4417 </span>  <span class="Comment"># on commenting the line is now wrapped</span>
+<span id="L4418" class="LineNr">4418 </span>  assume-console [
+<span id="L4419" class="LineNr">4419 </span>    left-click<span class="Constant"> 1</span>,<span class="Constant"> 7</span>
+<span id="L4420" class="LineNr">4420 </span>    press ctrl-slash
+<span id="L4421" class="LineNr">4421 </span>  ]
+<span id="L4422" class="LineNr">4422 </span>  run [
+<span id="L4423" class="LineNr">4423 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4424" class="LineNr">4424 </span>  ]
+<span id="L4425" class="LineNr">4425 </span>  screen-should-contain [
+<span id="L4426" class="LineNr">4426 </span>   <span class="Constant"> .          .</span>
+<span id="L4427" class="LineNr">4427 </span>   <span class="Constant"> .#? a↩     .</span>
+<span id="L4428" class="LineNr">4428 </span>   <span class="Constant"> .bcd       .</span>
+<span id="L4429" class="LineNr">4429 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
+<span id="L4430" class="LineNr">4430 </span>   <span class="Constant"> .          .</span>
+<span id="L4431" class="LineNr">4431 </span>  ]
+<span id="L4432" class="LineNr">4432 </span>]
+<span id="L4433" class="LineNr">4433 </span>
+<span id="L4434" class="LineNr">4434 </span><span class="muScenario">scenario</span> editor-uncomments-just-wrapping-line [
+<span id="L4435" class="LineNr">4435 </span>  <span class="Constant">local-scope</span>
+<span id="L4436" class="LineNr">4436 </span>  assume-screen <span class="Constant">10/width</span>, <span class="Constant">5/height</span>
+<span id="L4437" class="LineNr">4437 </span>  <span class="Comment"># editor starts out with a comment that wraps the line</span>
+<span id="L4438" class="LineNr">4438 </span>  e:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> <span class="Constant">[#? ab]</span>, <span class="Constant">0/left</span>, <span class="Constant">5/right</span>
+<span id="L4439" class="LineNr">4439 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
+<span id="L4440" class="LineNr">4440 </span>  screen-should-contain [
+<span id="L4441" class="LineNr">4441 </span>   <span class="Constant"> .          .</span>
+<span id="L4442" class="LineNr">4442 </span>   <span class="Constant"> .#? a↩     .</span>
+<span id="L4443" class="LineNr">4443 </span>   <span class="Constant"> .b         .</span>
+<span id="L4444" class="LineNr">4444 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
+<span id="L4445" class="LineNr">4445 </span>   <span class="Constant"> .          .</span>
+<span id="L4446" class="LineNr">4446 </span>  ]
+<span id="L4447" class="LineNr">4447 </span>  $clear-trace
+<span id="L4448" class="LineNr">4448 </span>  <span class="Comment"># on uncommenting the line is no longer wrapped</span>
+<span id="L4449" class="LineNr">4449 </span>  assume-console [
+<span id="L4450" class="LineNr">4450 </span>    left-click<span class="Constant"> 1</span>,<span class="Constant"> 7</span>
+<span id="L4451" class="LineNr">4451 </span>    press ctrl-slash
+<span id="L4452" class="LineNr">4452 </span>  ]
+<span id="L4453" class="LineNr">4453 </span>  run [
+<span id="L4454" class="LineNr">4454 </span>    <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
+<span id="L4455" class="LineNr">4455 </span>  ]
+<span id="L4456" class="LineNr">4456 </span>  screen-should-contain [
+<span id="L4457" class="LineNr">4457 </span>   <span class="Constant"> .          .</span>
+<span id="L4458" class="LineNr">4458 </span>   <span class="Constant"> .ab        .</span>
+<span id="L4459" class="LineNr">4459 </span>   <span class="Constant"> .╌╌╌╌╌     .</span>
+<span id="L4460" class="LineNr">4460 </span>   <span class="Constant"> .          .</span>
+<span id="L4461" class="LineNr">4461 </span>  ]
+<span id="L4462" class="LineNr">4462 </span>]
 </pre>
 </body>
 </html>
diff --git a/html/edit/004-programming-environment.mu.html b/html/edit/004-programming-environment.mu.html
index 34437128..dc0aa10e 100644
--- a/html/edit/004-programming-environment.mu.html
+++ b/html/edit/004-programming-environment.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -68,10 +68,10 @@ if ('onhashchange' in window) {
 <span id="L6" class="LineNr">  6 </span><span class="muRecipe">def!</span> main [
 <span id="L7" class="LineNr">  7 </span>  <span class="Constant">local-scope</span>
 <span id="L8" class="LineNr">  8 </span>  open-console
-<span id="L9" class="LineNr">  9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a> <span class="Constant">0/screen</span>  <span class="Comment"># non-scrolling app</span>
-<span id="L10" class="LineNr"> 10 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <span class="Constant">0/filesystem</span>, <span class="Constant">0/screen</span>
-<span id="L11" class="LineNr"> 11 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <span class="Constant">0/screen</span>, env, <a href='001-editor.mu.html#L107'>render</a>
-<span id="L12" class="LineNr"> 12 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <span class="Constant">0/screen</span>, <span class="Constant">0/console</span>, env, <span class="Constant">0/filesystem</span>
+<span id="L9" class="LineNr">  9 </span>  <a href='../081print.mu.html#L46'>clear-screen</a><span class="Constant"> null/screen</span>  <span class="Comment"># non-scrolling app</span>
+<span id="L10" class="LineNr"> 10 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a><span class="Constant"> null/filesystem, null/screen</span>
+<span id="L11" class="LineNr"> 11 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a><span class="Constant"> null/screen,</span> env, <a href='001-editor.mu.html#L109'>render</a>
+<span id="L12" class="LineNr"> 12 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a><span class="Constant"> null/screen, null/console,</span> env,<span class="Constant"> null/filesystem</span>
 <span id="L13" class="LineNr"> 13 </span>]
 <span id="L14" class="LineNr"> 14 </span>
 <span id="L15" class="LineNr"> 15 </span><span class="muData">container</span> environment [
@@ -94,7 +94,7 @@ if ('onhashchange' in window) {
 <span id="L32" class="LineNr"> 32 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L51'>new-editor</a> test-sandbox-editor-contents, sandbox-left, width/right
 <span id="L33" class="LineNr"> 33 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">recipes:offset</span>, recipes
 <span id="L34" class="LineNr"> 34 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">current-sandbox:offset</span>, current-sandbox
-<span id="L35" class="LineNr"> 35 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">sandbox-in-focus?:offset</span>, <span class="Constant">0/false</span>
+<span id="L35" class="LineNr"> 35 </span>  *result <span class="Special">&lt;-</span> put *result, <span class="Constant">sandbox-in-focus?:offset</span>,<span class="Constant"> false</span>
 <span id="L36" class="LineNr"> 36 </span><span class="Constant">  <a href='004-programming-environment.mu.html#L36'>&lt;programming-environment-initialization&gt;</a></span>
 <span id="L37" class="LineNr"> 37 </span>]
 <span id="L38" class="LineNr"> 38 </span>
@@ -107,8 +107,8 @@ if ('onhashchange' in window) {
 <span id="L45" class="LineNr"> 45 </span>  <span class="Comment"># if we fall behind we'll stop updating the screen, but then we have to</span>
 <span id="L46" class="LineNr"> 46 </span>  <span class="Comment"># render the entire screen when we catch up.</span>
 <span id="L47" class="LineNr"> 47 </span>  <span class="Comment"># todo: test this</span>
-<span id="L48" class="LineNr"> 48 </span>  render-recipes-on-no-more-events?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
-<span id="L49" class="LineNr"> 49 </span>  render-sandboxes-on-no-more-events?:bool <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L48" class="LineNr"> 48 </span>  render-recipes-on-no-more-events?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
+<span id="L49" class="LineNr"> 49 </span>  render-sandboxes-on-no-more-events?:bool <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L50" class="LineNr"> 50 </span>  <span class="Delimiter">{</span>
 <span id="L51" class="LineNr"> 51 </span>    <span class="Comment"># looping over each (keyboard or touch) event as it occurs</span>
 <span id="L52" class="LineNr"> 52 </span><span class="Constant">    +next-event</span>
@@ -175,13 +175,13 @@ if ('onhashchange' in window) {
 <span id="L113" class="LineNr">113 </span>        <span class="muControl">break-if</span> more-events?
 <span id="L114" class="LineNr">114 </span>        <span class="Delimiter">{</span>
 <span id="L115" class="LineNr">115 </span>          <span class="muControl">break-unless</span> render-recipes-on-no-more-events?
-<span id="L116" class="LineNr">116 </span>          render-recipes-on-no-more-events? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
-<span id="L117" class="LineNr">117 </span>          <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L116" class="LineNr">116 </span>          render-recipes-on-no-more-events? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
+<span id="L117" class="LineNr">117 </span>          <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L118" class="LineNr">118 </span>        <span class="Delimiter">}</span>
 <span id="L119" class="LineNr">119 </span>        <span class="Delimiter">{</span>
 <span id="L120" class="LineNr">120 </span>          <span class="muControl">break-unless</span> render-sandboxes-on-no-more-events?
-<span id="L121" class="LineNr">121 </span>          render-sandboxes-on-no-more-events? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
-<span id="L122" class="LineNr">122 </span>          <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L121" class="LineNr">121 </span>          render-sandboxes-on-no-more-events? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
+<span id="L122" class="LineNr">122 </span>          <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L123" class="LineNr">123 </span>        <span class="Delimiter">}</span>
 <span id="L124" class="LineNr">124 </span>      <span class="Delimiter">}</span>
 <span id="L125" class="LineNr">125 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
@@ -225,8 +225,8 @@ if ('onhashchange' in window) {
 <span id="L163" class="LineNr">163 </span>  <a href='../081print.mu.html#L782'>screen-height</a>:num <span class="Special">&lt;-</span> <a href='../081print.mu.html#L782'>screen-height</a> <a href='../081print.mu.html#L16'>screen</a>
 <span id="L164" class="LineNr">164 </span>  right:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">right:offset</span>
 <span id="L165" class="LineNr">165 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
-<span id="L166" class="LineNr">166 </span>  <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
-<span id="L167" class="LineNr">167 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L166" class="LineNr">166 </span>  <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> copy curr  <span class="Comment"># just in case curr becomes null and we can't compute prev</span>
+<span id="L167" class="LineNr">167 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L168" class="LineNr">168 </span>  color:num <span class="Special">&lt;-</span> copy <span class="Constant">7/white</span>
 <span id="L169" class="LineNr">169 </span>  row:num <span class="Special">&lt;-</span> copy <span class="Constant">1/top</span>
 <span id="L170" class="LineNr">170 </span>  column:num <span class="Special">&lt;-</span> copy left
@@ -248,7 +248,7 @@ if ('onhashchange' in window) {
 <span id="L186" class="LineNr">186 </span>    <span class="Comment"># editor.cursor-row and editor.cursor-column based on</span>
 <span id="L187" class="LineNr">187 </span>    <span class="Comment"># old-before-cursor</span>
 <span id="L188" class="LineNr">188 </span>    <span class="Delimiter">{</span>
-<span id="L189" class="LineNr">189 </span>      at-cursor?:bool <span class="Special">&lt;-</span> equal old-before-cursor, <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L189" class="LineNr">189 </span>      at-cursor?:bool <span class="Special">&lt;-</span> equal old-before-cursor, <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L190" class="LineNr">190 </span>      <span class="muControl">break-unless</span> at-cursor?
 <span id="L191" class="LineNr">191 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, row
 <span id="L192" class="LineNr">192 </span>      *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-column:offset</span>, column
@@ -266,8 +266,8 @@ if ('onhashchange' in window) {
 <span id="L204" class="LineNr">204 </span>      row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
 <span id="L205" class="LineNr">205 </span>      column <span class="Special">&lt;-</span> copy left
 <span id="L206" class="LineNr">206 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> move-cursor <a href='../081print.mu.html#L16'>screen</a>, row, column
-<span id="L207" class="LineNr">207 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L208" class="LineNr">208 </span>      <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L207" class="LineNr">207 </span>      curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L208" class="LineNr">208 </span>      <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L209" class="LineNr">209 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
 <span id="L210" class="LineNr">210 </span>    <span class="Delimiter">}</span>
 <span id="L211" class="LineNr">211 </span>    <span class="Delimiter">{</span>
@@ -285,8 +285,8 @@ if ('onhashchange' in window) {
 <span id="L223" class="LineNr">223 </span>     <span class="muControl"> loop</span> <span class="Constant">+next-character</span>
 <span id="L224" class="LineNr">224 </span>    <span class="Delimiter">}</span>
 <span id="L225" class="LineNr">225 </span>    print <a href='../081print.mu.html#L16'>screen</a>, c, color
-<span id="L226" class="LineNr">226 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L227" class="LineNr">227 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> <a href='../065duplex_list.mu.html#L32'>prev</a>
+<span id="L226" class="LineNr">226 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L227" class="LineNr">227 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> <a href='../065duplex_list.mu.html#L38'>prev</a>
 <span id="L228" class="LineNr">228 </span>    column <span class="Special">&lt;-</span> add column,<span class="Constant"> 1</span>
 <span id="L229" class="LineNr">229 </span>   <span class="muControl"> loop</span>
 <span id="L230" class="LineNr">230 </span>  <span class="Delimiter">}</span>
@@ -337,7 +337,7 @@ if ('onhashchange' in window) {
 <span id="L275" class="LineNr">275 </span>    ]
 <span id="L276" class="LineNr">276 </span>  ]
 <span id="L277" class="LineNr">277 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[def]</span>  <span class="Comment"># contents of sandbox</span>
-<span id="L278" class="LineNr">278 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L278" class="LineNr">278 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L279" class="LineNr">279 </span>  <span class="Comment"># type one letter in each of them</span>
 <span id="L280" class="LineNr">280 </span>  assume-console [
 <span id="L281" class="LineNr">281 </span>    left-click<span class="Constant"> 1</span>,<span class="Constant"> 1</span>
@@ -387,7 +387,7 @@ if ('onhashchange' in window) {
 <span id="L325" class="LineNr">325 </span>    ]
 <span id="L326" class="LineNr">326 </span>  ]
 <span id="L327" class="LineNr">327 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[def]</span>
-<span id="L328" class="LineNr">328 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L328" class="LineNr">328 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L329" class="LineNr">329 </span>  <span class="Comment"># initialize programming environment and highlight cursor</span>
 <span id="L330" class="LineNr">330 </span>  assume-console <span class="Constant">[]</span>
 <span id="L331" class="LineNr">331 </span>  run [
@@ -432,7 +432,7 @@ if ('onhashchange' in window) {
 <span id="L370" class="LineNr">370 </span>  test-sandbox-editor-contents:text <span class="Special">&lt;-</span> new <span class="Constant">[abc</span>
 <span id="L371" class="LineNr">371 </span><span class="Constant">def]</span>
 <span id="L372" class="LineNr">372 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, test-sandbox-editor-contents
-<span id="L373" class="LineNr">373 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L373" class="LineNr">373 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L374" class="LineNr">374 </span>  screen-should-contain [
 <span id="L375" class="LineNr">375 </span>   <span class="Constant"> .           run (F4)           .</span>
 <span id="L376" class="LineNr">376 </span>   <span class="Constant"> .               ╎abc           .</span>
@@ -504,7 +504,7 @@ if ('onhashchange' in window) {
 <span id="L442" class="LineNr">442 </span>  <span class="Comment"># draw dotted line after recipes</span>
 <span id="L443" class="LineNr">443 </span>  <a href='002-typing.mu.html#L1114'>draw-horizontal</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right, <span class="Constant">9480/horizontal-dotted</span>
 <span id="L444" class="LineNr">444 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L445" class="LineNr">445 </span>  <a href='001-editor.mu.html#L209'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
+<span id="L445" class="LineNr">445 </span>  <a href='001-editor.mu.html#L211'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
 <span id="L446" class="LineNr">446 </span>  <span class="Comment">#</span>
 <span id="L447" class="LineNr">447 </span>  <a href='../081print.mu.html#L515'>assert-no-scroll</a> <a href='../081print.mu.html#L16'>screen</a>, old-top-idx
 <span id="L448" class="LineNr">448 </span>]
@@ -522,7 +522,7 @@ if ('onhashchange' in window) {
 <span id="L460" class="LineNr">460 </span>  <span class="Comment"># draw solid line after code (you'll see why in later layers)</span>
 <span id="L461" class="LineNr">461 </span>  <a href='002-typing.mu.html#L1114'>draw-horizontal</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
 <span id="L462" class="LineNr">462 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L463" class="LineNr">463 </span>  <a href='001-editor.mu.html#L209'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
+<span id="L463" class="LineNr">463 </span>  <a href='001-editor.mu.html#L211'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
 <span id="L464" class="LineNr">464 </span>  <span class="Comment">#</span>
 <span id="L465" class="LineNr">465 </span>  <a href='../081print.mu.html#L515'>assert-no-scroll</a> <a href='../081print.mu.html#L16'>screen</a>, old-top-idx
 <span id="L466" class="LineNr">466 </span>]
diff --git a/html/edit/005-sandbox.mu.html b/html/edit/005-sandbox.mu.html
index 93fec922..ab45522e 100644
--- a/html/edit/005-sandbox.mu.html
+++ b/html/edit/005-sandbox.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -72,11 +72,11 @@ if ('onhashchange' in window) {
 <span id="L10" class="LineNr">  10 </span><span class="muRecipe">def!</span> main [
 <span id="L11" class="LineNr">  11 </span>  <span class="Constant">local-scope</span>
 <span id="L12" class="LineNr">  12 </span>  open-console
-<span id="L13" class="LineNr">  13 </span>  <a href='../081print.mu.html#L46'>clear-screen</a> <span class="Constant">0/screen</span>  <span class="Comment"># non-scrolling app</span>
-<span id="L14" class="LineNr">  14 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <span class="Constant">0/filesystem</span>, <span class="Constant">0/screen</span>
-<span id="L15" class="LineNr">  15 </span>  env <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L473'>restore-sandboxes</a> env, <span class="Constant">0/filesystem</span>
-<span id="L16" class="LineNr">  16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <span class="Constant">0/screen</span>, env, <a href='001-editor.mu.html#L107'>render</a>
-<span id="L17" class="LineNr">  17 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <span class="Constant">0/screen</span>, <span class="Constant">0/console</span>, env, <span class="Constant">0/filesystem</span>
+<span id="L13" class="LineNr">  13 </span>  <a href='../081print.mu.html#L46'>clear-screen</a><span class="Constant"> null/screen</span>  <span class="Comment"># non-scrolling app</span>
+<span id="L14" class="LineNr">  14 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a><span class="Constant"> null/filesystem, null/screen</span>
+<span id="L15" class="LineNr">  15 </span>  env <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L473'>restore-sandboxes</a> env,<span class="Constant"> null/filesystem</span>
+<span id="L16" class="LineNr">  16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a><span class="Constant"> null/screen,</span> env, <a href='001-editor.mu.html#L109'>render</a>
+<span id="L17" class="LineNr">  17 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a><span class="Constant"> null/screen, null/console,</span> env,<span class="Constant"> null/filesystem</span>
 <span id="L18" class="LineNr">  18 </span>]
 <span id="L19" class="LineNr">  19 </span>
 <span id="L20" class="LineNr">  20 </span><span class="muData">container</span> environment [
@@ -109,7 +109,7 @@ if ('onhashchange' in window) {
 <span id="L47" class="LineNr">  47 </span>  ]
 <span id="L48" class="LineNr">  48 </span>  <span class="Comment"># sandbox editor contains an instruction without storing outputs</span>
 <span id="L49" class="LineNr">  49 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[divide-with-remainder 11, 3]</span>
-<span id="L50" class="LineNr">  50 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L50" class="LineNr">  50 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L51" class="LineNr">  51 </span>  <span class="Comment"># run the code in the editors</span>
 <span id="L52" class="LineNr">  52 </span>  assume-console [
 <span id="L53" class="LineNr">  53 </span>    press F4
@@ -195,7 +195,7 @@ if ('onhashchange' in window) {
 <span id="L133" class="LineNr"> 133 </span>    error?:bool <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L146'>run-sandboxes</a> env, <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>
 <span id="L134" class="LineNr"> 134 </span>    <span class="Comment"># we could just render-all, but we do some work to minimize the number of prints to screen</span>
 <span id="L135" class="LineNr"> 135 </span><span class="Constant">    <a href='005-sandbox.mu.html#L135'>&lt;end-run-sandboxes-on-F4&gt;</a></span>
-<span id="L136" class="LineNr"> 136 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L136" class="LineNr"> 136 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L137" class="LineNr"> 137 </span>    <span class="Delimiter">{</span>
 <span id="L138" class="LineNr"> 138 </span>      <span class="muControl">break-if</span> error?
 <span id="L139" class="LineNr"> 139 </span>      <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L217'>update-status</a> <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[                 ]</span>, <span class="Constant">245/grey</span>
@@ -232,7 +232,7 @@ if ('onhashchange' in window) {
 <span id="L170" class="LineNr"> 170 </span>    <span class="Comment"># needs to be before running them, in case we die when running</span>
 <span id="L171" class="LineNr"> 171 </span>    <a href='005-sandbox.mu.html#L224'>save-sandboxes</a> env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L172" class="LineNr"> 172 </span>    <span class="Comment"># clear sandbox editor</span>
-<span id="L173" class="LineNr"> 173 </span>    init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> push <span class="Constant">167/§</span>, <span class="Constant">0/tail</span>
+<span id="L173" class="LineNr"> 173 </span>    init:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> push <span class="Constant">167/§</span>,<span class="Constant"> null</span>
 <span id="L174" class="LineNr"> 174 </span>    *current-sandbox <span class="Special">&lt;-</span> put *current-sandbox, <span class="Constant">data:offset</span>, init
 <span id="L175" class="LineNr"> 175 </span>    *current-sandbox <span class="Special">&lt;-</span> put *current-sandbox, <span class="Constant">top-of-screen:offset</span>, init
 <span id="L176" class="LineNr"> 176 </span>  <span class="Delimiter">}</span>
@@ -263,7 +263,7 @@ if ('onhashchange' in window) {
 <span id="L201" class="LineNr"> 201 </span>  in:text <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L681'>editor-contents</a> recipes
 <span id="L202" class="LineNr"> 202 </span>  <a href='../088file.mu.html#L11'>resources</a> <span class="Special">&lt;-</span> <a href='../088file.mu.html#L127'>dump</a> <a href='../088file.mu.html#L11'>resources</a>, <span class="Constant">[lesson/recipes.mu]</span>, in
 <span id="L203" class="LineNr"> 203 </span>  reload in
-<span id="L204" class="LineNr"> 204 </span>  errors-found? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L204" class="LineNr"> 204 </span>  errors-found? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L205" class="LineNr"> 205 </span>]
 <span id="L206" class="LineNr"> 206 </span>
 <span id="L207" class="LineNr"> 207 </span><span class="Comment"># replaced in a later layer</span>
@@ -330,7 +330,7 @@ if ('onhashchange' in window) {
 <span id="L268" class="LineNr"> 268 </span>  <a href='002-typing.mu.html#L1114'>draw-horizontal</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
 <span id="L269" class="LineNr"> 269 </span>  sandbox:&amp;:sandbox <span class="Special">&lt;-</span> get *env, <span class="Constant">sandbox:offset</span>
 <span id="L270" class="LineNr"> 270 </span>  row, <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L276'>render-sandboxes</a> <a href='../081print.mu.html#L16'>screen</a>, sandbox, left, right, row, render-from
-<span id="L271" class="LineNr"> 271 </span>  <a href='001-editor.mu.html#L224'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
+<span id="L271" class="LineNr"> 271 </span>  <a href='001-editor.mu.html#L226'>clear-rest-of-screen</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right
 <span id="L272" class="LineNr"> 272 </span>  <span class="Comment">#</span>
 <span id="L273" class="LineNr"> 273 </span>  <a href='../081print.mu.html#L515'>assert-no-scroll</a> <a href='../081print.mu.html#L16'>screen</a>, old-top-idx
 <span id="L274" class="LineNr"> 274 </span>]
@@ -420,7 +420,7 @@ if ('onhashchange' in window) {
 <span id="L358" class="LineNr"> 358 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
 <span id="L359" class="LineNr"> 359 </span>  env <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L473'>restore-sandboxes</a> env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L360" class="LineNr"> 360 </span>  run [
-<span id="L361" class="LineNr"> 361 </span>    <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L361" class="LineNr"> 361 </span>    <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L362" class="LineNr"> 362 </span>  ]
 <span id="L363" class="LineNr"> 363 </span>  screen-should-contain [
 <span id="L364" class="LineNr"> 364 </span>   <span class="Constant"> .                                                                                 run (F4)           .</span>
@@ -537,8 +537,8 @@ if ('onhashchange' in window) {
 <span id="L475" class="LineNr"> 475 </span>  <span class="Constant">load-inputs</span>
 <span id="L476" class="LineNr"> 476 </span>  <span class="Comment"># read all scenarios, pushing them to end of a list of scenarios</span>
 <span id="L477" class="LineNr"> 477 </span>  idx:num <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
-<span id="L478" class="LineNr"> 478 </span>  curr:&amp;:sandbox <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
-<span id="L479" class="LineNr"> 479 </span>  <a href='../065duplex_list.mu.html#L32'>prev</a>:&amp;:sandbox <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
+<span id="L478" class="LineNr"> 478 </span>  curr:&amp;:sandbox <span class="Special">&lt;-</span> copy<span class="Constant"> null</span>
+<span id="L479" class="LineNr"> 479 </span>  <a href='../065duplex_list.mu.html#L38'>prev</a>:&amp;:sandbox <span class="Special">&lt;-</span> copy<span class="Constant"> null</span>
 <span id="L480" class="LineNr"> 480 </span>  <span class="Delimiter">{</span>
 <span id="L481" class="LineNr"> 481 </span>    filename:text <span class="Special">&lt;-</span> append <span class="Constant">[lesson/]</span>, idx
 <span id="L482" class="LineNr"> 482 </span>    contents:text <span class="Special">&lt;-</span> <a href='../088file.mu.html#L38'>slurp</a> <a href='../088file.mu.html#L11'>resources</a>, filename
@@ -557,7 +557,7 @@ if ('onhashchange' in window) {
 <span id="L495" class="LineNr"> 495 </span>      *prev <span class="Special">&lt;-</span> put *prev, <span class="Constant">next-sandbox:offset</span>, curr
 <span id="L496" class="LineNr"> 496 </span>    <span class="Delimiter">}</span>
 <span id="L497" class="LineNr"> 497 </span>    idx <span class="Special">&lt;-</span> add idx,<span class="Constant"> 1</span>
-<span id="L498" class="LineNr"> 498 </span>    <a href='../065duplex_list.mu.html#L32'>prev</a> <span class="Special">&lt;-</span> copy curr
+<span id="L498" class="LineNr"> 498 </span>    <a href='../065duplex_list.mu.html#L38'>prev</a> <span class="Special">&lt;-</span> copy curr
 <span id="L499" class="LineNr"> 499 </span>   <span class="muControl"> loop</span>
 <span id="L500" class="LineNr"> 500 </span>  <span class="Delimiter">}</span>
 <span id="L501" class="LineNr"> 501 </span>  <span class="Comment"># update sandbox count</span>
@@ -648,7 +648,7 @@ if ('onhashchange' in window) {
 <span id="L586" class="LineNr"> 586 </span>  ]
 <span id="L587" class="LineNr"> 587 </span>  <span class="Comment"># sandbox editor contains an instruction without storing outputs</span>
 <span id="L588" class="LineNr"> 588 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L589" class="LineNr"> 589 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L589" class="LineNr"> 589 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L590" class="LineNr"> 590 </span>  $clear-trace
 <span id="L591" class="LineNr"> 591 </span>  <span class="Comment"># run the code in the editors</span>
 <span id="L592" class="LineNr"> 592 </span>  assume-console [
@@ -673,7 +673,7 @@ if ('onhashchange' in window) {
 <span id="L611" class="LineNr"> 611 </span>  ]
 <span id="L612" class="LineNr"> 612 </span>  <span class="Comment"># no need to update editor</span>
 <span id="L613" class="LineNr"> 613 </span>  trace-should-not-contain [
-<span id="L614" class="LineNr"> 614 </span>    app: <a href='001-editor.mu.html#L107'>render</a> recipes
+<span id="L614" class="LineNr"> 614 </span>    app: <a href='001-editor.mu.html#L109'>render</a> recipes
 <span id="L615" class="LineNr"> 615 </span>  ]
 <span id="L616" class="LineNr"> 616 </span>  <span class="Comment"># make a change (incrementing one of the args to 'add'), then rerun</span>
 <span id="L617" class="LineNr"> 617 </span>  $clear-trace
@@ -714,7 +714,7 @@ if ('onhashchange' in window) {
 <span id="L652" class="LineNr"> 652 </span>  ]
 <span id="L653" class="LineNr"> 653 </span>  <span class="Comment"># sandbox editor contains an instruction</span>
 <span id="L654" class="LineNr"> 654 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[print <a href='../081print.mu.html#L16'>screen</a>, 4]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L655" class="LineNr"> 655 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L655" class="LineNr"> 655 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L656" class="LineNr"> 656 </span>  <span class="Comment"># run the code in the editor</span>
 <span id="L657" class="LineNr"> 657 </span>  assume-console [
 <span id="L658" class="LineNr"> 658 </span>    press F4
@@ -747,13 +747,13 @@ if ('onhashchange' in window) {
 <span id="L685" class="LineNr"> 685 </span>  curr:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
 <span id="L686" class="LineNr"> 686 </span>  <span class="Comment"># skip § sentinel</span>
 <span id="L687" class="LineNr"> 687 </span>  assert curr, <span class="Constant">[editor without data is illegal; must have at least a sentinel]</span>
-<span id="L688" class="LineNr"> 688 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
-<span id="L689" class="LineNr"> 689 </span>  <span class="muControl">return-unless</span> curr,<span class="Constant"> 0</span>
+<span id="L688" class="LineNr"> 688 </span>  curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
+<span id="L689" class="LineNr"> 689 </span>  <span class="muControl">return-unless</span> curr,<span class="Constant"> null</span>
 <span id="L690" class="LineNr"> 690 </span>  <span class="Delimiter">{</span>
 <span id="L691" class="LineNr"> 691 </span>    <span class="muControl">break-unless</span> curr
 <span id="L692" class="LineNr"> 692 </span>    c:char <span class="Special">&lt;-</span> get *curr, <span class="Constant">value:offset</span>
 <span id="L693" class="LineNr"> 693 </span>    buf <span class="Special">&lt;-</span> append buf, c
-<span id="L694" class="LineNr"> 694 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> curr
+<span id="L694" class="LineNr"> 694 </span>    curr <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> curr
 <span id="L695" class="LineNr"> 695 </span>   <span class="muControl"> loop</span>
 <span id="L696" class="LineNr"> 696 </span>  <span class="Delimiter">}</span>
 <span id="L697" class="LineNr"> 697 </span>  result <span class="Special">&lt;-</span> <a href='../061text.mu.html#L338'>buffer-to-array</a> buf
@@ -786,7 +786,7 @@ if ('onhashchange' in window) {
 <span id="L724" class="LineNr"> 724 </span>  assume-resources [
 <span id="L725" class="LineNr"> 725 </span>  ]
 <span id="L726" class="LineNr"> 726 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L727" class="LineNr"> 727 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L727" class="LineNr"> 727 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L728" class="LineNr"> 728 </span>  assume-console [
 <span id="L729" class="LineNr"> 729 </span>    press enter
 <span id="L730" class="LineNr"> 730 </span>    press down-arrow
@@ -809,7 +809,7 @@ if ('onhashchange' in window) {
 <span id="L747" class="LineNr"> 747 </span>  assume-resources [
 <span id="L748" class="LineNr"> 748 </span>  ]
 <span id="L749" class="LineNr"> 749 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L750" class="LineNr"> 750 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L750" class="LineNr"> 750 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L751" class="LineNr"> 751 </span>  assume-console [
 <span id="L752" class="LineNr"> 752 </span>    press enter
 <span id="L753" class="LineNr"> 753 </span>    press up-arrow
@@ -835,14 +835,14 @@ if ('onhashchange' in window) {
 <span id="L773" class="LineNr"> 773 </span>  assume-resources [
 <span id="L774" class="LineNr"> 774 </span>  ]
 <span id="L775" class="LineNr"> 775 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L776" class="LineNr"> 776 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L776" class="LineNr"> 776 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L777" class="LineNr"> 777 </span>  assume-console [
 <span id="L778" class="LineNr"> 778 </span>    <span class="Comment"># add a line</span>
 <span id="L779" class="LineNr"> 779 </span>    press enter
 <span id="L780" class="LineNr"> 780 </span>    <span class="Comment"># cursor back to top line</span>
 <span id="L781" class="LineNr"> 781 </span>    press up-arrow
 <span id="L782" class="LineNr"> 782 </span>    <span class="Comment"># try to scroll</span>
-<span id="L783" class="LineNr"> 783 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>  <span class="Comment"># or ctrl-f</span>
+<span id="L783" class="LineNr"> 783 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>  <span class="Comment"># or ctrl-f</span>
 <span id="L784" class="LineNr"> 784 </span>  ]
 <span id="L785" class="LineNr"> 785 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L786" class="LineNr"> 786 </span>  <span class="Comment"># no scroll, and cursor remains at top line</span>
@@ -863,7 +863,7 @@ if ('onhashchange' in window) {
 <span id="L801" class="LineNr"> 801 </span>  ]
 <span id="L802" class="LineNr"> 802 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[ab</span>
 <span id="L803" class="LineNr"> 803 </span><span class="Constant">cd]</span>
-<span id="L804" class="LineNr"> 804 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L804" class="LineNr"> 804 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L805" class="LineNr"> 805 </span>  assume-console [
 <span id="L806" class="LineNr"> 806 </span>    <span class="Comment"># add a line</span>
 <span id="L807" class="LineNr"> 807 </span>    press enter
@@ -895,7 +895,7 @@ if ('onhashchange' in window) {
 <span id="L833" class="LineNr"> 833 </span>  assume-resources [
 <span id="L834" class="LineNr"> 834 </span>  ]
 <span id="L835" class="LineNr"> 835 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 2, 2]</span>
-<span id="L836" class="LineNr"> 836 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L836" class="LineNr"> 836 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L837" class="LineNr"> 837 </span>  assume-console [
 <span id="L838" class="LineNr"> 838 </span>    <span class="Comment"># create a sandbox</span>
 <span id="L839" class="LineNr"> 839 </span>    press F4
@@ -911,7 +911,7 @@ if ('onhashchange' in window) {
 <span id="L849" class="LineNr"> 849 </span>  <span class="Comment"># switch to sandbox window and hit 'page-down'</span>
 <span id="L850" class="LineNr"> 850 </span>  assume-console [
 <span id="L851" class="LineNr"> 851 </span>    press ctrl-n
-<span id="L852" class="LineNr"> 852 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L852" class="LineNr"> 852 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L853" class="LineNr"> 853 </span>  ]
 <span id="L854" class="LineNr"> 854 </span>  run [
 <span id="L855" class="LineNr"> 855 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -929,7 +929,7 @@ if ('onhashchange' in window) {
 <span id="L867" class="LineNr"> 867 </span>  ]
 <span id="L868" class="LineNr"> 868 </span>  <span class="Comment"># hit 'page-up'</span>
 <span id="L869" class="LineNr"> 869 </span>  assume-console [
-<span id="L870" class="LineNr"> 870 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L870" class="LineNr"> 870 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L871" class="LineNr"> 871 </span>  ]
 <span id="L872" class="LineNr"> 872 </span>  run [
 <span id="L873" class="LineNr"> 873 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -964,7 +964,7 @@ if ('onhashchange' in window) {
 <span id="L902" class="LineNr"> 902 </span>      render-from <span class="Special">&lt;-</span> add render-from,<span class="Constant"> 1</span>
 <span id="L903" class="LineNr"> 903 </span>      *env <span class="Special">&lt;-</span> put *env, <span class="Constant">render-from:offset</span>, render-from
 <span id="L904" class="LineNr"> 904 </span>    <span class="Delimiter">}</span>
-<span id="L905" class="LineNr"> 905 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L905" class="LineNr"> 905 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L906" class="LineNr"> 906 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L907" class="LineNr"> 907 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L908" class="LineNr"> 908 </span>  <span class="Delimiter">}</span>
@@ -994,26 +994,26 @@ if ('onhashchange' in window) {
 <span id="L932" class="LineNr"> 932 </span>    <span class="muControl">break-if</span> at-beginning?
 <span id="L933" class="LineNr"> 933 </span>    render-from <span class="Special">&lt;-</span> subtract render-from,<span class="Constant"> 1</span>
 <span id="L934" class="LineNr"> 934 </span>    *env <span class="Special">&lt;-</span> put *env, <span class="Constant">render-from:offset</span>, render-from
-<span id="L935" class="LineNr"> 935 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L935" class="LineNr"> 935 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L936" class="LineNr"> 936 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L937" class="LineNr"> 937 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L938" class="LineNr"> 938 </span>  <span class="Delimiter">}</span>
 <span id="L939" class="LineNr"> 939 </span>]
 <span id="L940" class="LineNr"> 940 </span>
 <span id="L941" class="LineNr"> 941 </span><span class="Comment"># sandbox belonging to 'env' whose next-sandbox is 'in'</span>
-<span id="L942" class="LineNr"> 942 </span><span class="Comment"># return 0 if there's no such sandbox, either because 'in' doesn't exist in 'env', or because it's the first sandbox</span>
+<span id="L942" class="LineNr"> 942 </span><span class="Comment"># return null if there's no such sandbox, either because 'in' doesn't exist in 'env', or because it's the first sandbox</span>
 <span id="L943" class="LineNr"> 943 </span><span class="muRecipe">def</span> <a href='005-sandbox.mu.html#L943'>previous-sandbox</a> env:&amp;:environment, in:&amp;:sandbox<span class="muRecipe"> -&gt; </span>out:&amp;:sandbox [
 <span id="L944" class="LineNr"> 944 </span>  <span class="Constant">local-scope</span>
 <span id="L945" class="LineNr"> 945 </span>  <span class="Constant">load-inputs</span>
 <span id="L946" class="LineNr"> 946 </span>  curr:&amp;:sandbox <span class="Special">&lt;-</span> get *env, <span class="Constant">sandbox:offset</span>
-<span id="L947" class="LineNr"> 947 </span>  <span class="muControl">return-unless</span> curr, <span class="Constant">0/nil</span>
-<span id="L948" class="LineNr"> 948 </span>  <a href='../065duplex_list.mu.html#L25'>next</a>:&amp;:sandbox <span class="Special">&lt;-</span> get *curr, <span class="Constant">next-sandbox:offset</span>
+<span id="L947" class="LineNr"> 947 </span>  <span class="muControl">return-unless</span> curr,<span class="Constant"> null</span>
+<span id="L948" class="LineNr"> 948 </span>  <a href='../065duplex_list.mu.html#L31'>next</a>:&amp;:sandbox <span class="Special">&lt;-</span> get *curr, <span class="Constant">next-sandbox:offset</span>
 <span id="L949" class="LineNr"> 949 </span>  <span class="Delimiter">{</span>
-<span id="L950" class="LineNr"> 950 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L25'>next</a>, <span class="Constant">0/nil</span>
-<span id="L951" class="LineNr"> 951 </span>    found?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L25'>next</a>, in
+<span id="L950" class="LineNr"> 950 </span>    <span class="muControl">return-unless</span> <a href='../065duplex_list.mu.html#L31'>next</a>,<span class="Constant"> null</span>
+<span id="L951" class="LineNr"> 951 </span>    found?:bool <span class="Special">&lt;-</span> equal <a href='../065duplex_list.mu.html#L31'>next</a>, in
 <span id="L952" class="LineNr"> 952 </span>    <span class="muControl">break-if</span> found?
-<span id="L953" class="LineNr"> 953 </span>    curr <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L25'>next</a>
-<span id="L954" class="LineNr"> 954 </span>    <a href='../065duplex_list.mu.html#L25'>next</a> <span class="Special">&lt;-</span> get *curr, <span class="Constant">next-sandbox:offset</span>
+<span id="L953" class="LineNr"> 953 </span>    curr <span class="Special">&lt;-</span> copy <a href='../065duplex_list.mu.html#L31'>next</a>
+<span id="L954" class="LineNr"> 954 </span>    <a href='../065duplex_list.mu.html#L31'>next</a> <span class="Special">&lt;-</span> get *curr, <span class="Constant">next-sandbox:offset</span>
 <span id="L955" class="LineNr"> 955 </span>   <span class="muControl"> loop</span>
 <span id="L956" class="LineNr"> 956 </span>  <span class="Delimiter">}</span>
 <span id="L957" class="LineNr"> 957 </span> <span class="muControl"> return</span> curr
@@ -1027,7 +1027,7 @@ if ('onhashchange' in window) {
 <span id="L965" class="LineNr"> 965 </span>  assume-resources [
 <span id="L966" class="LineNr"> 966 </span>  ]
 <span id="L967" class="LineNr"> 967 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L968" class="LineNr"> 968 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L968" class="LineNr"> 968 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L969" class="LineNr"> 969 </span>  <span class="Comment"># create 2 sandboxes</span>
 <span id="L970" class="LineNr"> 970 </span>  assume-console [
 <span id="L971" class="LineNr"> 971 </span>    press ctrl-n
@@ -1053,7 +1053,7 @@ if ('onhashchange' in window) {
 <span id="L991" class="LineNr"> 991 </span>  ]
 <span id="L992" class="LineNr"> 992 </span>  <span class="Comment"># hit 'page-down'</span>
 <span id="L993" class="LineNr"> 993 </span>  assume-console [
-<span id="L994" class="LineNr"> 994 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L994" class="LineNr"> 994 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L995" class="LineNr"> 995 </span>  ]
 <span id="L996" class="LineNr"> 996 </span>  run [
 <span id="L997" class="LineNr"> 997 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1075,7 +1075,7 @@ if ('onhashchange' in window) {
 <span id="L1013" class="LineNr">1013 </span>  ]
 <span id="L1014" class="LineNr">1014 </span>  <span class="Comment"># hit 'page-down' again</span>
 <span id="L1015" class="LineNr">1015 </span>  assume-console [
-<span id="L1016" class="LineNr">1016 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1016" class="LineNr">1016 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1017" class="LineNr">1017 </span>  ]
 <span id="L1018" class="LineNr">1018 </span>  run [
 <span id="L1019" class="LineNr">1019 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1092,7 +1092,7 @@ if ('onhashchange' in window) {
 <span id="L1030" class="LineNr">1030 </span>  ]
 <span id="L1031" class="LineNr">1031 </span>  <span class="Comment"># hit 'page-down' again</span>
 <span id="L1032" class="LineNr">1032 </span>  assume-console [
-<span id="L1033" class="LineNr">1033 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1033" class="LineNr">1033 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1034" class="LineNr">1034 </span>  ]
 <span id="L1035" class="LineNr">1035 </span>  run [
 <span id="L1036" class="LineNr">1036 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1109,7 +1109,7 @@ if ('onhashchange' in window) {
 <span id="L1047" class="LineNr">1047 </span>  ]
 <span id="L1048" class="LineNr">1048 </span>  <span class="Comment"># hit 'page-up'</span>
 <span id="L1049" class="LineNr">1049 </span>  assume-console [
-<span id="L1050" class="LineNr">1050 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L1050" class="LineNr">1050 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L1051" class="LineNr">1051 </span>  ]
 <span id="L1052" class="LineNr">1052 </span>  run [
 <span id="L1053" class="LineNr">1053 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1128,7 +1128,7 @@ if ('onhashchange' in window) {
 <span id="L1066" class="LineNr">1066 </span>  ]
 <span id="L1067" class="LineNr">1067 </span>  <span class="Comment"># hit 'page-up' again</span>
 <span id="L1068" class="LineNr">1068 </span>  assume-console [
-<span id="L1069" class="LineNr">1069 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L1069" class="LineNr">1069 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L1070" class="LineNr">1070 </span>  ]
 <span id="L1071" class="LineNr">1071 </span>  run [
 <span id="L1072" class="LineNr">1072 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1150,7 +1150,7 @@ if ('onhashchange' in window) {
 <span id="L1088" class="LineNr">1088 </span>  ]
 <span id="L1089" class="LineNr">1089 </span>  <span class="Comment"># hit 'page-up' again</span>
 <span id="L1090" class="LineNr">1090 </span>  assume-console [
-<span id="L1091" class="LineNr">1091 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L1091" class="LineNr">1091 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L1092" class="LineNr">1092 </span>  ]
 <span id="L1093" class="LineNr">1093 </span>  run [
 <span id="L1094" class="LineNr">1094 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1180,7 +1180,7 @@ if ('onhashchange' in window) {
 <span id="L1118" class="LineNr">1118 </span>  assume-resources [
 <span id="L1119" class="LineNr">1119 </span>  ]
 <span id="L1120" class="LineNr">1120 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L1121" class="LineNr">1121 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L1121" class="LineNr">1121 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L1122" class="LineNr">1122 </span>  <span class="Comment"># create a sandbox</span>
 <span id="L1123" class="LineNr">1123 </span>  assume-console [
 <span id="L1124" class="LineNr">1124 </span>    press ctrl-n
@@ -1200,7 +1200,7 @@ if ('onhashchange' in window) {
 <span id="L1138" class="LineNr">1138 </span>  ]
 <span id="L1139" class="LineNr">1139 </span>  <span class="Comment"># hit 'page-down' and 'page-up' a couple of times. sandbox index should be stable</span>
 <span id="L1140" class="LineNr">1140 </span>  assume-console [
-<span id="L1141" class="LineNr">1141 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1141" class="LineNr">1141 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1142" class="LineNr">1142 </span>  ]
 <span id="L1143" class="LineNr">1143 </span>  run [
 <span id="L1144" class="LineNr">1144 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1218,7 +1218,7 @@ if ('onhashchange' in window) {
 <span id="L1156" class="LineNr">1156 </span>  ]
 <span id="L1157" class="LineNr">1157 </span>  <span class="Comment"># hit 'page-up' again</span>
 <span id="L1158" class="LineNr">1158 </span>  assume-console [
-<span id="L1159" class="LineNr">1159 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L1159" class="LineNr">1159 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L1160" class="LineNr">1160 </span>  ]
 <span id="L1161" class="LineNr">1161 </span>  run [
 <span id="L1162" class="LineNr">1162 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -1236,7 +1236,7 @@ if ('onhashchange' in window) {
 <span id="L1174" class="LineNr">1174 </span>  ]
 <span id="L1175" class="LineNr">1175 </span>  <span class="Comment"># hit 'page-down'</span>
 <span id="L1176" class="LineNr">1176 </span>  assume-console [
-<span id="L1177" class="LineNr">1177 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1177" class="LineNr">1177 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1178" class="LineNr">1178 </span>  ]
 <span id="L1179" class="LineNr">1179 </span>  run [
 <span id="L1180" class="LineNr">1180 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
diff --git a/html/edit/006-sandbox-copy.mu.html b/html/edit/006-sandbox-copy.mu.html
index 57c581a7..fe119f1e 100644
--- a/html/edit/006-sandbox-copy.mu.html
+++ b/html/edit/006-sandbox-copy.mu.html
@@ -15,16 +15,16 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.Delimiter { color: #800080; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
-.Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -70,7 +70,7 @@ if ('onhashchange' in window) {
 <span id="L9" class="LineNr">  9 </span>  assume-resources [
 <span id="L10" class="LineNr"> 10 </span>  ]
 <span id="L11" class="LineNr"> 11 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 1, 1]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L12" class="LineNr"> 12 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L12" class="LineNr"> 12 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L13" class="LineNr"> 13 </span>  <span class="Comment"># run it</span>
 <span id="L14" class="LineNr"> 14 </span>  assume-console [
 <span id="L15" class="LineNr"> 15 </span>    press F4
@@ -131,7 +131,7 @@ if ('onhashchange' in window) {
 <span id="L70" class="LineNr"> 70 </span>  assume-resources [
 <span id="L71" class="LineNr"> 71 </span>  ]
 <span id="L72" class="LineNr"> 72 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 1, 1]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L73" class="LineNr"> 73 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L73" class="LineNr"> 73 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L74" class="LineNr"> 74 </span>  <span class="Comment"># run it</span>
 <span id="L75" class="LineNr"> 75 </span>  assume-console [
 <span id="L76" class="LineNr"> 76 </span>    press F4
@@ -191,7 +191,7 @@ if ('onhashchange' in window) {
 <span id="L130" class="LineNr">130 </span>    <span class="muControl">break-unless</span> copy?
 <span id="L131" class="LineNr">131 </span>    copy?, env <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L159'>try-copy-sandbox</a> click-row, env
 <span id="L132" class="LineNr">132 </span>    <span class="muControl">break-unless</span> copy?
-<span id="L133" class="LineNr">133 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L133" class="LineNr">133 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L134" class="LineNr">134 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L135" class="LineNr">135 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L136" class="LineNr">136 </span>  <span class="Delimiter">}</span>
@@ -203,7 +203,7 @@ if ('onhashchange' in window) {
 <span id="L142" class="LineNr">142 </span>  <span class="Constant">load-inputs</span>
 <span id="L143" class="LineNr">143 </span>  <span class="Comment"># are we below the sandbox editor?</span>
 <span id="L144" class="LineNr">144 </span>  click-sandbox-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L190'>click-on-sandbox-area?</a> click-row, click-column, env
-<span id="L145" class="LineNr">145 </span>  <span class="muControl">return-unless</span> click-sandbox-area?, <span class="Constant">0/false</span>
+<span id="L145" class="LineNr">145 </span>  <span class="muControl">return-unless</span> click-sandbox-area?,<span class="Constant"> false</span>
 <span id="L146" class="LineNr">146 </span>  <span class="Comment"># narrower, is the click in the columns spanning the 'copy' button?</span>
 <span id="L147" class="LineNr">147 </span>  first-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L148" class="LineNr">148 </span>  assert first-sandbox, <span class="Constant">[!!]</span>
@@ -211,7 +211,7 @@ if ('onhashchange' in window) {
 <span id="L150" class="LineNr">150 </span>  sandbox-right-margin:num <span class="Special">&lt;-</span> get *first-sandbox, <span class="Constant">right:offset</span>
 <span id="L151" class="LineNr">151 </span>  _, _, copy-button-left:num, copy-button-right:num <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L376'>sandbox-menu-columns</a> sandbox-left-margin, sandbox-right-margin
 <span id="L152" class="LineNr">152 </span>  copy-button-vertical-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L211'>within-range?</a> click-column, copy-button-left, copy-button-right
-<span id="L153" class="LineNr">153 </span>  <span class="muControl">return-unless</span> copy-button-vertical-area?, <span class="Constant">0/false</span>
+<span id="L153" class="LineNr">153 </span>  <span class="muControl">return-unless</span> copy-button-vertical-area?,<span class="Constant"> false</span>
 <span id="L154" class="LineNr">154 </span>  <span class="Comment"># finally, is sandbox editor empty?</span>
 <span id="L155" class="LineNr">155 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L156" class="LineNr">156 </span>  result <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L203'>empty-editor?</a> current-sandbox
@@ -222,15 +222,15 @@ if ('onhashchange' in window) {
 <span id="L161" class="LineNr">161 </span>  <span class="Constant">load-inputs</span>
 <span id="L162" class="LineNr">162 </span>  <span class="Comment"># identify the sandbox to copy, if the click was actually on the 'copy' button</span>
 <span id="L163" class="LineNr">163 </span>  sandbox:&amp;:sandbox <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L175'>find-sandbox</a> env, click-row
-<span id="L164" class="LineNr">164 </span>  <span class="muControl">return-unless</span> sandbox, <span class="Constant">0/false</span>
-<span id="L165" class="LineNr">165 </span>  clicked-on-copy-button? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L164" class="LineNr">164 </span>  <span class="muControl">return-unless</span> sandbox,<span class="Constant"> false</span>
+<span id="L165" class="LineNr">165 </span>  clicked-on-copy-button? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L166" class="LineNr">166 </span>  text:text <span class="Special">&lt;-</span> get *sandbox, <span class="Constant">data:offset</span>
 <span id="L167" class="LineNr">167 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L168" class="LineNr">168 </span>  current-sandbox <span class="Special">&lt;-</span> <a href='001-editor.mu.html#L72'>insert-text</a> current-sandbox, text
 <span id="L169" class="LineNr">169 </span>  <span class="Comment"># reset scroll</span>
 <span id="L170" class="LineNr">170 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">render-from:offset</span>,<span class="Constant"> -1</span>
 <span id="L171" class="LineNr">171 </span>  <span class="Comment"># position cursor in sandbox editor</span>
-<span id="L172" class="LineNr">172 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>, <span class="Constant">1/true</span>
+<span id="L172" class="LineNr">172 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>,<span class="Constant"> true</span>
 <span id="L173" class="LineNr">173 </span>]
 <span id="L174" class="LineNr">174 </span>
 <span id="L175" class="LineNr">175 </span><span class="muRecipe">def</span> <a href='006-sandbox-copy.mu.html#L175'>find-sandbox</a> env:&amp;:environment, click-row:num<span class="muRecipe"> -&gt; </span>result:&amp;:sandbox [
@@ -245,7 +245,7 @@ if ('onhashchange' in window) {
 <span id="L184" class="LineNr">184 </span>    curr-sandbox <span class="Special">&lt;-</span> get *curr-sandbox, <span class="Constant">next-sandbox:offset</span>
 <span id="L185" class="LineNr">185 </span>   <span class="muControl"> loop</span>
 <span id="L186" class="LineNr">186 </span>  <span class="Delimiter">}</span>
-<span id="L187" class="LineNr">187 </span> <span class="muControl"> return</span> <span class="Constant">0/not-found</span>
+<span id="L187" class="LineNr">187 </span> <span class="muControl"> return</span><span class="Constant"> null/not-found</span>
 <span id="L188" class="LineNr">188 </span>]
 <span id="L189" class="LineNr">189 </span>
 <span id="L190" class="LineNr">190 </span><span class="muRecipe">def</span> <a href='006-sandbox-copy.mu.html#L190'>click-on-sandbox-area?</a> click-row:num, click-column:num, env:&amp;:environment<span class="muRecipe"> -&gt; </span>result:bool [
@@ -254,9 +254,9 @@ if ('onhashchange' in window) {
 <span id="L193" class="LineNr">193 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L194" class="LineNr">194 </span>  sandbox-left-margin:num <span class="Special">&lt;-</span> get *current-sandbox, <span class="Constant">left:offset</span>
 <span id="L195" class="LineNr">195 </span>  on-sandbox-side?:bool <span class="Special">&lt;-</span> greater-or-equal click-column, sandbox-left-margin
-<span id="L196" class="LineNr">196 </span>  <span class="muControl">return-unless</span> on-sandbox-side?, <span class="Constant">0/false</span>
+<span id="L196" class="LineNr">196 </span>  <span class="muControl">return-unless</span> on-sandbox-side?,<span class="Constant"> false</span>
 <span id="L197" class="LineNr">197 </span>  first-sandbox:&amp;:sandbox <span class="Special">&lt;-</span> get *env, <span class="Constant">sandbox:offset</span>
-<span id="L198" class="LineNr">198 </span>  <span class="muControl">return-unless</span> first-sandbox, <span class="Constant">0/false</span>
+<span id="L198" class="LineNr">198 </span>  <span class="muControl">return-unless</span> first-sandbox,<span class="Constant"> false</span>
 <span id="L199" class="LineNr">199 </span>  first-sandbox-begins:num <span class="Special">&lt;-</span> get *first-sandbox, <span class="Constant">starting-row-on-screen:offset</span>
 <span id="L200" class="LineNr">200 </span>  result <span class="Special">&lt;-</span> greater-or-equal click-row, first-sandbox-begins
 <span id="L201" class="LineNr">201 </span>]
@@ -265,7 +265,7 @@ if ('onhashchange' in window) {
 <span id="L204" class="LineNr">204 </span>  <span class="Constant">local-scope</span>
 <span id="L205" class="LineNr">205 </span>  <span class="Constant">load-inputs</span>
 <span id="L206" class="LineNr">206 </span>  head:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L207" class="LineNr">207 </span>  first:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> head
+<span id="L207" class="LineNr">207 </span>  first:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> head
 <span id="L208" class="LineNr">208 </span>  result <span class="Special">&lt;-</span> not first
 <span id="L209" class="LineNr">209 </span>]
 <span id="L210" class="LineNr">210 </span>
@@ -285,7 +285,7 @@ if ('onhashchange' in window) {
 <span id="L224" class="LineNr">224 </span>  assume-resources [
 <span id="L225" class="LineNr">225 </span>  ]
 <span id="L226" class="LineNr">226 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 1, 1]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L227" class="LineNr">227 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L227" class="LineNr">227 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L228" class="LineNr">228 </span>  <span class="Comment"># run it</span>
 <span id="L229" class="LineNr">229 </span>  assume-console [
 <span id="L230" class="LineNr">230 </span>    press F4
@@ -350,7 +350,7 @@ if ('onhashchange' in window) {
 <span id="L289" class="LineNr">289 </span>  assume-resources [
 <span id="L290" class="LineNr">290 </span>  ]
 <span id="L291" class="LineNr">291 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 1, 1]</span>  <span class="Comment"># contents of sandbox editor</span>
-<span id="L292" class="LineNr">292 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L292" class="LineNr">292 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L293" class="LineNr">293 </span>  <span class="Comment"># run it</span>
 <span id="L294" class="LineNr">294 </span>  assume-console [
 <span id="L295" class="LineNr">295 </span>    press F4
@@ -410,8 +410,8 @@ if ('onhashchange' in window) {
 <span id="L349" class="LineNr">349 </span>    <span class="muControl">break-unless</span> copy?
 <span id="L350" class="LineNr">350 </span>    modified?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L375'>prepend-sandbox-into-recipe-side</a> click-row, env
 <span id="L351" class="LineNr">351 </span>    <span class="muControl">break-unless</span> modified?
-<span id="L352" class="LineNr">352 </span>    *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>, <span class="Constant">0/false</span>
-<span id="L353" class="LineNr">353 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L352" class="LineNr">352 </span>    *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>,<span class="Constant"> false</span>
+<span id="L353" class="LineNr">353 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L354" class="LineNr">354 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L355" class="LineNr">355 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L356" class="LineNr">356 </span>  <span class="Delimiter">}</span>
@@ -423,7 +423,7 @@ if ('onhashchange' in window) {
 <span id="L362" class="LineNr">362 </span>  <span class="Constant">load-inputs</span>
 <span id="L363" class="LineNr">363 </span>  <span class="Comment"># are we below the sandbox editor?</span>
 <span id="L364" class="LineNr">364 </span>  click-sandbox-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L190'>click-on-sandbox-area?</a> click-row, click-column, env
-<span id="L365" class="LineNr">365 </span>  <span class="muControl">return-unless</span> click-sandbox-area?, <span class="Constant">0/false</span>
+<span id="L365" class="LineNr">365 </span>  <span class="muControl">return-unless</span> click-sandbox-area?,<span class="Constant"> false</span>
 <span id="L366" class="LineNr">366 </span>  <span class="Comment"># narrower, is the click in the columns spanning the 'copy' button?</span>
 <span id="L367" class="LineNr">367 </span>  first-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L368" class="LineNr">368 </span>  assert first-sandbox, <span class="Constant">[!!]</span>
@@ -437,7 +437,7 @@ if ('onhashchange' in window) {
 <span id="L376" class="LineNr">376 </span>  <span class="Constant">local-scope</span>
 <span id="L377" class="LineNr">377 </span>  <span class="Constant">load-inputs</span>
 <span id="L378" class="LineNr">378 </span>  sandbox:&amp;:sandbox <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L175'>find-sandbox</a> env, click-row
-<span id="L379" class="LineNr">379 </span>  <span class="muControl">return-unless</span> sandbox, <span class="Constant">0/false</span>
+<span id="L379" class="LineNr">379 </span>  <span class="muControl">return-unless</span> sandbox,<span class="Constant"> false</span>
 <span id="L380" class="LineNr">380 </span>  recipe-editor:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">recipes:offset</span>
 <span id="L381" class="LineNr">381 </span>  recipe-data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *recipe-editor, <span class="Constant">data:offset</span>
 <span id="L382" class="LineNr">382 </span>  <span class="Comment"># make the newly inserted code easy to delineate</span>
@@ -452,7 +452,7 @@ if ('onhashchange' in window) {
 <span id="L391" class="LineNr">391 </span>  *recipe-editor <span class="Special">&lt;-</span> put *recipe-editor, <span class="Constant">before-cursor:offset</span>, recipe-data
 <span id="L392" class="LineNr">392 </span>  *recipe-editor <span class="Special">&lt;-</span> put *recipe-editor, <span class="Constant">cursor-row:offset</span>,<span class="Constant"> 1</span>
 <span id="L393" class="LineNr">393 </span>  *recipe-editor <span class="Special">&lt;-</span> put *recipe-editor, <span class="Constant">cursor-column:offset</span>,<span class="Constant"> 0</span>
-<span id="L394" class="LineNr">394 </span> <span class="muControl"> return</span> <span class="Constant">1/true</span>
+<span id="L394" class="LineNr">394 </span> <span class="muControl"> return</span><span class="Constant"> true</span>
 <span id="L395" class="LineNr">395 </span>]
 </pre>
 </body>
diff --git a/html/edit/007-sandbox-delete.mu.html b/html/edit/007-sandbox-delete.mu.html
index d51294bc..74ad4eb6 100644
--- a/html/edit/007-sandbox-delete.mu.html
+++ b/html/edit/007-sandbox-delete.mu.html
@@ -15,16 +15,16 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.Delimiter { color: #800080; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
-.Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -68,7 +68,7 @@ if ('onhashchange' in window) {
 <span id="L7" class="LineNr">  7 </span>  assume-resources [
 <span id="L8" class="LineNr">  8 </span>  ]
 <span id="L9" class="LineNr">  9 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L10" class="LineNr"> 10 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L10" class="LineNr"> 10 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L11" class="LineNr"> 11 </span>  <span class="Comment"># run a few commands</span>
 <span id="L12" class="LineNr"> 12 </span>  assume-console [
 <span id="L13" class="LineNr"> 13 </span>    left-click<span class="Constant"> 1</span>,<span class="Constant"> 75</span>
@@ -134,7 +134,7 @@ if ('onhashchange' in window) {
 <span id="L73" class="LineNr"> 73 </span>    <span class="muControl">break-unless</span> delete?
 <span id="L74" class="LineNr"> 74 </span>    delete?, env <span class="Special">&lt;-</span> <a href='007-sandbox-delete.mu.html#L98'>try-delete-sandbox</a> click-row, env
 <span id="L75" class="LineNr"> 75 </span>    <span class="muControl">break-unless</span> delete?
-<span id="L76" class="LineNr"> 76 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L76" class="LineNr"> 76 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L77" class="LineNr"> 77 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L78" class="LineNr"> 78 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L79" class="LineNr"> 79 </span>  <span class="Delimiter">}</span>
@@ -146,7 +146,7 @@ if ('onhashchange' in window) {
 <span id="L85" class="LineNr"> 85 </span>  <span class="Constant">load-inputs</span>
 <span id="L86" class="LineNr"> 86 </span>  <span class="Comment"># are we below the sandbox editor?</span>
 <span id="L87" class="LineNr"> 87 </span>  click-sandbox-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L190'>click-on-sandbox-area?</a> click-row, click-column, env
-<span id="L88" class="LineNr"> 88 </span>  <span class="muControl">return-unless</span> click-sandbox-area?, <span class="Constant">0/false</span>
+<span id="L88" class="LineNr"> 88 </span>  <span class="muControl">return-unless</span> click-sandbox-area?,<span class="Constant"> false</span>
 <span id="L89" class="LineNr"> 89 </span>  <span class="Comment"># narrower, is the click in the columns spanning the 'copy' button?</span>
 <span id="L90" class="LineNr"> 90 </span>  first-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L91" class="LineNr"> 91 </span>  assert first-sandbox, <span class="Constant">[!!]</span>
@@ -161,8 +161,8 @@ if ('onhashchange' in window) {
 <span id="L100" class="LineNr">100 </span>  <span class="Constant">load-inputs</span>
 <span id="L101" class="LineNr">101 </span>  <span class="Comment"># identify the sandbox to delete, if the click was actually on the 'delete' button</span>
 <span id="L102" class="LineNr">102 </span>  sandbox:&amp;:sandbox <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L175'>find-sandbox</a> env, click-row
-<span id="L103" class="LineNr">103 </span>  <span class="muControl">return-unless</span> sandbox, <span class="Constant">0/false</span>
-<span id="L104" class="LineNr">104 </span>  clicked-on-delete-button? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L103" class="LineNr">103 </span>  <span class="muControl">return-unless</span> sandbox,<span class="Constant"> false</span>
+<span id="L104" class="LineNr">104 </span>  clicked-on-delete-button? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L105" class="LineNr">105 </span>  env <span class="Special">&lt;-</span> <a href='007-sandbox-delete.mu.html#L108'>delete-sandbox</a> env, sandbox
 <span id="L106" class="LineNr">106 </span>]
 <span id="L107" class="LineNr">107 </span>
@@ -216,7 +216,7 @@ if ('onhashchange' in window) {
 <span id="L155" class="LineNr">155 </span>  assume-resources [
 <span id="L156" class="LineNr">156 </span>  ]
 <span id="L157" class="LineNr">157 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L158" class="LineNr">158 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L158" class="LineNr">158 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L159" class="LineNr">159 </span>  <span class="Comment"># create 2 sandboxes and scroll to second</span>
 <span id="L160" class="LineNr">160 </span>  assume-console [
 <span id="L161" class="LineNr">161 </span>    press ctrl-n
@@ -224,7 +224,7 @@ if ('onhashchange' in window) {
 <span id="L163" class="LineNr">163 </span>    press F4
 <span id="L164" class="LineNr">164 </span>    type <span class="Constant">[add 1, 1]</span>
 <span id="L165" class="LineNr">165 </span>    press F4
-<span id="L166" class="LineNr">166 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L166" class="LineNr">166 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L167" class="LineNr">167 </span>  ]
 <span id="L168" class="LineNr">168 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L169" class="LineNr">169 </span>  screen-should-contain [
@@ -263,7 +263,7 @@ if ('onhashchange' in window) {
 <span id="L202" class="LineNr">202 </span>  assume-resources [
 <span id="L203" class="LineNr">203 </span>  ]
 <span id="L204" class="LineNr">204 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L205" class="LineNr">205 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L205" class="LineNr">205 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L206" class="LineNr">206 </span>  <span class="Comment"># create 2 sandboxes and scroll to second</span>
 <span id="L207" class="LineNr">207 </span>  assume-console [
 <span id="L208" class="LineNr">208 </span>    press ctrl-n
@@ -271,7 +271,7 @@ if ('onhashchange' in window) {
 <span id="L210" class="LineNr">210 </span>    press F4
 <span id="L211" class="LineNr">211 </span>    type <span class="Constant">[add 1, 1]</span>
 <span id="L212" class="LineNr">212 </span>    press F4
-<span id="L213" class="LineNr">213 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L213" class="LineNr">213 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L214" class="LineNr">214 </span>  ]
 <span id="L215" class="LineNr">215 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L216" class="LineNr">216 </span>  screen-should-contain [
@@ -310,7 +310,7 @@ if ('onhashchange' in window) {
 <span id="L249" class="LineNr">249 </span>  assume-resources [
 <span id="L250" class="LineNr">250 </span>  ]
 <span id="L251" class="LineNr">251 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L252" class="LineNr">252 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L252" class="LineNr">252 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L253" class="LineNr">253 </span>  <span class="Comment"># create 2 sandboxes and scroll to second</span>
 <span id="L254" class="LineNr">254 </span>  assume-console [
 <span id="L255" class="LineNr">255 </span>    press ctrl-n
@@ -318,8 +318,8 @@ if ('onhashchange' in window) {
 <span id="L257" class="LineNr">257 </span>    press F4
 <span id="L258" class="LineNr">258 </span>    type <span class="Constant">[add 1, 1]</span>
 <span id="L259" class="LineNr">259 </span>    press F4
-<span id="L260" class="LineNr">260 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L261" class="LineNr">261 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L260" class="LineNr">260 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L261" class="LineNr">261 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L262" class="LineNr">262 </span>  ]
 <span id="L263" class="LineNr">263 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L264" class="LineNr">264 </span>  screen-should-contain [
@@ -359,7 +359,7 @@ if ('onhashchange' in window) {
 <span id="L298" class="LineNr">298 </span>  assume-resources [
 <span id="L299" class="LineNr">299 </span>  ]
 <span id="L300" class="LineNr">300 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L301" class="LineNr">301 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L301" class="LineNr">301 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L302" class="LineNr">302 </span>  <span class="Comment"># create 2 sandboxes</span>
 <span id="L303" class="LineNr">303 </span>  assume-console [
 <span id="L304" class="LineNr">304 </span>    press ctrl-n
@@ -384,8 +384,8 @@ if ('onhashchange' in window) {
 <span id="L323" class="LineNr">323 </span>  <span class="Comment"># delete the second sandbox, then try to scroll down twice</span>
 <span id="L324" class="LineNr">324 </span>  assume-console [
 <span id="L325" class="LineNr">325 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 99</span>
-<span id="L326" class="LineNr">326 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L327" class="LineNr">327 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L326" class="LineNr">326 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L327" class="LineNr">327 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L328" class="LineNr">328 </span>  ]
 <span id="L329" class="LineNr">329 </span>  run [
 <span id="L330" class="LineNr">330 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
diff --git a/html/edit/008-sandbox-edit.mu.html b/html/edit/008-sandbox-edit.mu.html
index a38ea948..62de3b4d 100644
--- a/html/edit/008-sandbox-edit.mu.html
+++ b/html/edit/008-sandbox-edit.mu.html
@@ -15,16 +15,16 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.Delimiter { color: #800080; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
-.Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -69,7 +69,7 @@ if ('onhashchange' in window) {
 <span id="L8" class="LineNr">  8 </span>  assume-resources [
 <span id="L9" class="LineNr">  9 </span>  ]
 <span id="L10" class="LineNr"> 10 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 2, 2]</span>
-<span id="L11" class="LineNr"> 11 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L11" class="LineNr"> 11 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L12" class="LineNr"> 12 </span>  <span class="Comment"># run it</span>
 <span id="L13" class="LineNr"> 13 </span>  assume-console [
 <span id="L14" class="LineNr"> 14 </span>    press F4
@@ -122,7 +122,7 @@ if ('onhashchange' in window) {
 <span id="L61" class="LineNr"> 61 </span>  assume-resources [
 <span id="L62" class="LineNr"> 62 </span>  ]
 <span id="L63" class="LineNr"> 63 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[add 2, 2]</span>
-<span id="L64" class="LineNr"> 64 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L64" class="LineNr"> 64 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L65" class="LineNr"> 65 </span>  <span class="Comment"># run it</span>
 <span id="L66" class="LineNr"> 66 </span>  assume-console [
 <span id="L67" class="LineNr"> 67 </span>    press F4
@@ -174,7 +174,7 @@ if ('onhashchange' in window) {
 <span id="L113" class="LineNr">113 </span>    <span class="muControl">break-unless</span> edit?
 <span id="L114" class="LineNr">114 </span>    edit?, env <span class="Special">&lt;-</span> <a href='008-sandbox-edit.mu.html#L142'>try-edit-sandbox</a> click-row, env
 <span id="L115" class="LineNr">115 </span>    <span class="muControl">break-unless</span> edit?
-<span id="L116" class="LineNr">116 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L116" class="LineNr">116 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L117" class="LineNr">117 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L118" class="LineNr">118 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L119" class="LineNr">119 </span>  <span class="Delimiter">}</span>
@@ -186,7 +186,7 @@ if ('onhashchange' in window) {
 <span id="L125" class="LineNr">125 </span>  <span class="Constant">load-inputs</span>
 <span id="L126" class="LineNr">126 </span>  <span class="Comment"># are we below the sandbox editor?</span>
 <span id="L127" class="LineNr">127 </span>  click-sandbox-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L190'>click-on-sandbox-area?</a> click-row, click-column, env
-<span id="L128" class="LineNr">128 </span>  <span class="muControl">return-unless</span> click-sandbox-area?, <span class="Constant">0/false</span>
+<span id="L128" class="LineNr">128 </span>  <span class="muControl">return-unless</span> click-sandbox-area?,<span class="Constant"> false</span>
 <span id="L129" class="LineNr">129 </span>  <span class="Comment"># narrower, is the click in the columns spanning the 'edit' button?</span>
 <span id="L130" class="LineNr">130 </span>  first-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L131" class="LineNr">131 </span>  assert first-sandbox, <span class="Constant">[!!]</span>
@@ -194,7 +194,7 @@ if ('onhashchange' in window) {
 <span id="L133" class="LineNr">133 </span>  sandbox-right-margin:num <span class="Special">&lt;-</span> get *first-sandbox, <span class="Constant">right:offset</span>
 <span id="L134" class="LineNr">134 </span>  edit-button-left:num, edit-button-right:num, _ <span class="Special">&lt;-</span> <a href='005-sandbox.mu.html#L376'>sandbox-menu-columns</a> sandbox-left-margin, sandbox-right-margin
 <span id="L135" class="LineNr">135 </span>  edit-button-vertical-area?:bool <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L211'>within-range?</a> click-column, edit-button-left, edit-button-right
-<span id="L136" class="LineNr">136 </span>  <span class="muControl">return-unless</span> edit-button-vertical-area?, <span class="Constant">0/false</span>
+<span id="L136" class="LineNr">136 </span>  <span class="muControl">return-unless</span> edit-button-vertical-area?,<span class="Constant"> false</span>
 <span id="L137" class="LineNr">137 </span>  <span class="Comment"># finally, is sandbox editor empty?</span>
 <span id="L138" class="LineNr">138 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
 <span id="L139" class="LineNr">139 </span>  result <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L203'>empty-editor?</a> current-sandbox
@@ -205,8 +205,8 @@ if ('onhashchange' in window) {
 <span id="L144" class="LineNr">144 </span>  <span class="Constant">load-inputs</span>
 <span id="L145" class="LineNr">145 </span>  <span class="Comment"># identify the sandbox to edit, if the click was actually on the 'edit' button</span>
 <span id="L146" class="LineNr">146 </span>  sandbox:&amp;:sandbox <span class="Special">&lt;-</span> <a href='006-sandbox-copy.mu.html#L175'>find-sandbox</a> env, click-row
-<span id="L147" class="LineNr">147 </span>  <span class="muControl">return-unless</span> sandbox, <span class="Constant">0/false</span>
-<span id="L148" class="LineNr">148 </span>  clicked-on-edit-button? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L147" class="LineNr">147 </span>  <span class="muControl">return-unless</span> sandbox,<span class="Constant"> false</span>
+<span id="L148" class="LineNr">148 </span>  clicked-on-edit-button? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L149" class="LineNr">149 </span>  <span class="Comment"># 'edit' button = 'copy' button + 'delete' button</span>
 <span id="L150" class="LineNr">150 </span>  text:text <span class="Special">&lt;-</span> get *sandbox, <span class="Constant">data:offset</span>
 <span id="L151" class="LineNr">151 </span>  current-sandbox:&amp;:editor <span class="Special">&lt;-</span> get *env, <span class="Constant">current-sandbox:offset</span>
@@ -215,7 +215,7 @@ if ('onhashchange' in window) {
 <span id="L154" class="LineNr">154 </span>  <span class="Comment"># reset scroll</span>
 <span id="L155" class="LineNr">155 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">render-from:offset</span>,<span class="Constant"> -1</span>
 <span id="L156" class="LineNr">156 </span>  <span class="Comment"># position cursor in sandbox editor</span>
-<span id="L157" class="LineNr">157 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>, <span class="Constant">1/true</span>
+<span id="L157" class="LineNr">157 </span>  *env <span class="Special">&lt;-</span> put *env, <span class="Constant">sandbox-in-focus?:offset</span>,<span class="Constant"> true</span>
 <span id="L158" class="LineNr">158 </span>]
 <span id="L159" class="LineNr">159 </span>
 <span id="L160" class="LineNr">160 </span><span class="muScenario">scenario</span> sandbox-with-print-can-be-edited [
@@ -227,7 +227,7 @@ if ('onhashchange' in window) {
 <span id="L166" class="LineNr">166 </span>  ]
 <span id="L167" class="LineNr">167 </span>  <span class="Comment"># right editor contains a print instruction</span>
 <span id="L168" class="LineNr">168 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[print <a href='../081print.mu.html#L16'>screen</a>, 4]</span>
-<span id="L169" class="LineNr">169 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L169" class="LineNr">169 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L170" class="LineNr">170 </span>  <span class="Comment"># run the sandbox</span>
 <span id="L171" class="LineNr">171 </span>  assume-console [
 <span id="L172" class="LineNr">172 </span>    press F4
@@ -272,7 +272,7 @@ if ('onhashchange' in window) {
 <span id="L211" class="LineNr">211 </span>  assume-resources [
 <span id="L212" class="LineNr">212 </span>  ]
 <span id="L213" class="LineNr">213 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L214" class="LineNr">214 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L214" class="LineNr">214 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L215" class="LineNr">215 </span>  <span class="Comment"># create 2 sandboxes and scroll to second</span>
 <span id="L216" class="LineNr">216 </span>  assume-console [
 <span id="L217" class="LineNr">217 </span>    press ctrl-n
@@ -280,8 +280,8 @@ if ('onhashchange' in window) {
 <span id="L219" class="LineNr">219 </span>    press F4
 <span id="L220" class="LineNr">220 </span>    type <span class="Constant">[add 1, 1]</span>
 <span id="L221" class="LineNr">221 </span>    press F4
-<span id="L222" class="LineNr">222 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L223" class="LineNr">223 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L222" class="LineNr">222 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L223" class="LineNr">223 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L224" class="LineNr">224 </span>  ]
 <span id="L225" class="LineNr">225 </span>  <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
 <span id="L226" class="LineNr">226 </span>  screen-should-contain [
@@ -321,7 +321,7 @@ if ('onhashchange' in window) {
 <span id="L260" class="LineNr">260 </span>  assume-resources [
 <span id="L261" class="LineNr">261 </span>  ]
 <span id="L262" class="LineNr">262 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L263" class="LineNr">263 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L263" class="LineNr">263 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L264" class="LineNr">264 </span>  <span class="Comment"># create 2 sandboxes</span>
 <span id="L265" class="LineNr">265 </span>  assume-console [
 <span id="L266" class="LineNr">266 </span>    press ctrl-n
@@ -366,9 +366,9 @@ if ('onhashchange' in window) {
 <span id="L305" class="LineNr">305 </span>  ]
 <span id="L306" class="LineNr">306 </span>  <span class="Comment"># now try to scroll past end</span>
 <span id="L307" class="LineNr">307 </span>  assume-console [
-<span id="L308" class="LineNr">308 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L309" class="LineNr">309 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L310" class="LineNr">310 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L308" class="LineNr">308 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L309" class="LineNr">309 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L310" class="LineNr">310 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L311" class="LineNr">311 </span>  ]
 <span id="L312" class="LineNr">312 </span>  run [
 <span id="L313" class="LineNr">313 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
diff --git a/html/edit/009-sandbox-test.mu.html b/html/edit/009-sandbox-test.mu.html
index 88dca874..5b70530e 100644
--- a/html/edit/009-sandbox-test.mu.html
+++ b/html/edit/009-sandbox-test.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -75,7 +75,7 @@ if ('onhashchange' in window) {
 <span id="L13" class="LineNr"> 13 </span>    ]
 <span id="L14" class="LineNr"> 14 </span>  ]
 <span id="L15" class="LineNr"> 15 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L16" class="LineNr"> 16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L16" class="LineNr"> 16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L17" class="LineNr"> 17 </span>  <span class="Comment"># run it</span>
 <span id="L18" class="LineNr"> 18 </span>  assume-console [
 <span id="L19" class="LineNr"> 19 </span>    press F4
@@ -233,9 +233,9 @@ if ('onhashchange' in window) {
 <span id="L171" class="LineNr">171 </span>  <span class="Delimiter">}</span>
 <span id="L172" class="LineNr">172 </span>  <span class="Comment"># return sandbox if click is in its output region</span>
 <span id="L173" class="LineNr">173 </span>  response-starting-row:num <span class="Special">&lt;-</span> get *sandbox, <span class="Constant">response-starting-row-on-screen:offset</span>
-<span id="L174" class="LineNr">174 </span>  <span class="muControl">return-unless</span> response-starting-row, <span class="Constant">0/no-click-in-sandbox-output</span>, <span class="Constant">0/sandbox-index</span>
+<span id="L174" class="LineNr">174 </span>  <span class="muControl">return-unless</span> response-starting-row,<span class="Constant"> null/no-click-in-sandbox-output,</span> <span class="Constant">0/sandbox-index</span>
 <span id="L175" class="LineNr">175 </span>  click-in-response?:bool <span class="Special">&lt;-</span> greater-or-equal click-row, response-starting-row
-<span id="L176" class="LineNr">176 </span>  <span class="muControl">return-unless</span> click-in-response?, <span class="Constant">0/no-click-in-sandbox-output</span>, <span class="Constant">0/sandbox-index</span>
+<span id="L176" class="LineNr">176 </span>  <span class="muControl">return-unless</span> click-in-response?,<span class="Constant"> null/no-click-in-sandbox-output,</span> <span class="Constant">0/sandbox-index</span>
 <span id="L177" class="LineNr">177 </span> <span class="muControl"> return</span> sandbox, sandbox-index
 <span id="L178" class="LineNr">178 </span>]
 <span id="L179" class="LineNr">179 </span>
@@ -246,7 +246,7 @@ if ('onhashchange' in window) {
 <span id="L184" class="LineNr">184 </span>  <span class="Delimiter">{</span>
 <span id="L185" class="LineNr">185 </span>    <span class="Comment"># if expected-response is set, reset</span>
 <span id="L186" class="LineNr">186 </span>    <span class="muControl">break-unless</span> expected-response
-<span id="L187" class="LineNr">187 </span>    *sandbox <span class="Special">&lt;-</span> put *sandbox, <span class="Constant">expected-response:offset</span>,<span class="Constant"> 0</span>
+<span id="L187" class="LineNr">187 </span>    *sandbox <span class="Special">&lt;-</span> put *sandbox, <span class="Constant">expected-response:offset</span>,<span class="Constant"> null</span>
 <span id="L188" class="LineNr">188 </span>  <span class="Delimiter">}</span>
 <span id="L189" class="LineNr">189 </span>  <span class="Delimiter">{</span>
 <span id="L190" class="LineNr">190 </span>    <span class="Comment"># if not, set expected response to the current response</span>
diff --git a/html/edit/010-sandbox-trace.mu.html b/html/edit/010-sandbox-trace.mu.html
index d0834aa1..5d4404c1 100644
--- a/html/edit/010-sandbox-trace.mu.html
+++ b/html/edit/010-sandbox-trace.mu.html
@@ -16,16 +16,16 @@ a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
 .muControl { color: #c0a020; }
-.muScenario { color: #00af00; }
+.muRecipe { color: #ff8700; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
+.muData { color: #ffff00; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
-.muRecipe { color: #ff8700; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -75,7 +75,7 @@ if ('onhashchange' in window) {
 <span id="L13" class="LineNr"> 13 </span>    ]
 <span id="L14" class="LineNr"> 14 </span>  ]
 <span id="L15" class="LineNr"> 15 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L16" class="LineNr"> 16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L16" class="LineNr"> 16 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L17" class="LineNr"> 17 </span>  <span class="Comment"># run it</span>
 <span id="L18" class="LineNr"> 18 </span>  assume-console [
 <span id="L19" class="LineNr"> 19 </span>    press F4
@@ -150,7 +150,7 @@ if ('onhashchange' in window) {
 <span id="L88" class="LineNr"> 88 </span>    ]
 <span id="L89" class="LineNr"> 89 </span>  ]
 <span id="L90" class="LineNr"> 90 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L91" class="LineNr"> 91 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L91" class="LineNr"> 91 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L92" class="LineNr"> 92 </span>  <span class="Comment"># run it</span>
 <span id="L93" class="LineNr"> 93 </span>  assume-console [
 <span id="L94" class="LineNr"> 94 </span>    press F4
@@ -195,7 +195,7 @@ if ('onhashchange' in window) {
 <span id="L133" class="LineNr">133 </span>  assume-resources [
 <span id="L134" class="LineNr">134 </span>  ]
 <span id="L135" class="LineNr">135 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[stash 123456789]</span>
-<span id="L136" class="LineNr">136 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L136" class="LineNr">136 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L137" class="LineNr">137 </span>  <span class="Comment"># create and expand the trace</span>
 <span id="L138" class="LineNr">138 </span>  assume-console [
 <span id="L139" class="LineNr">139 </span>    press F4
@@ -265,7 +265,7 @@ if ('onhashchange' in window) {
 <span id="L203" class="LineNr">203 </span>    x:bool <span class="Special">&lt;-</span> get *sandbox, <span class="Constant">display-trace?:offset</span>
 <span id="L204" class="LineNr">204 </span>    x <span class="Special">&lt;-</span> not x
 <span id="L205" class="LineNr">205 </span>    *sandbox <span class="Special">&lt;-</span> put *sandbox, <span class="Constant">display-trace?:offset</span>, x
-<span id="L206" class="LineNr">206 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L206" class="LineNr">206 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> render-sandbox-side <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L207" class="LineNr">207 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L468'>update-cursor</a> <a href='../081print.mu.html#L16'>screen</a>, recipes, current-sandbox, sandbox-in-focus?, env
 <span id="L208" class="LineNr">208 </span>   <span class="muControl"> loop</span> <span class="Constant">+next-event</span>
 <span id="L209" class="LineNr">209 </span>  <span class="Delimiter">}</span>
@@ -297,7 +297,7 @@ if ('onhashchange' in window) {
 <span id="L235" class="LineNr">235 </span>  click-on-sandbox-code?:bool <span class="Special">&lt;-</span> and click-above-response?, click-below-menu?
 <span id="L236" class="LineNr">236 </span>  <span class="Delimiter">{</span>
 <span id="L237" class="LineNr">237 </span>    <span class="muControl">break-if</span> click-on-sandbox-code?
-<span id="L238" class="LineNr">238 </span>   <span class="muControl"> return</span> <span class="Constant">0/no-click-in-sandbox-output</span>
+<span id="L238" class="LineNr">238 </span>   <span class="muControl"> return</span><span class="Constant"> null/no-click-in-sandbox-output</span>
 <span id="L239" class="LineNr">239 </span>  <span class="Delimiter">}</span>
 <span id="L240" class="LineNr">240 </span> <span class="muControl"> return</span> sandbox
 <span id="L241" class="LineNr">241 </span>]
diff --git a/html/edit/011-errors.mu.html b/html/edit/011-errors.mu.html
index 2a5511ac..96677150 100644
--- a/html/edit/011-errors.mu.html
+++ b/html/edit/011-errors.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -79,10 +79,10 @@ if ('onhashchange' in window) {
 <span id="L17" class="LineNr"> 17 </span>  <span class="Delimiter">{</span>
 <span id="L18" class="LineNr"> 18 </span>    <span class="muControl">break-unless</span> recipe-errors
 <span id="L19" class="LineNr"> 19 </span>    <a href='005-sandbox.mu.html#L217'>update-status</a> <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[errors found     ]</span>, <span class="Constant">1/red</span>
-<span id="L20" class="LineNr"> 20 </span>    errors-found? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L20" class="LineNr"> 20 </span>    errors-found? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L21" class="LineNr"> 21 </span>   <span class="muControl"> return</span>
 <span id="L22" class="LineNr"> 22 </span>  <span class="Delimiter">}</span>
-<span id="L23" class="LineNr"> 23 </span>  errors-found? <span class="Special">&lt;-</span> copy <span class="Constant">0/false</span>
+<span id="L23" class="LineNr"> 23 </span>  errors-found? <span class="Special">&lt;-</span> copy<span class="Constant"> false</span>
 <span id="L24" class="LineNr"> 24 </span>]
 <span id="L25" class="LineNr"> 25 </span>
 <span id="L26" class="LineNr"> 26 </span><span class="muRecipe">after</span> <span class="Constant"><a href='005-sandbox.mu.html#L132'>&lt;begin-run-sandboxes-on-F4&gt;</a></span> [
@@ -92,7 +92,7 @@ if ('onhashchange' in window) {
 <span id="L30" class="LineNr"> 30 </span>  <span class="Comment"># if there were recipe errors before, check if we can clear them</span>
 <span id="L31" class="LineNr"> 31 </span>  <span class="Delimiter">{</span>
 <span id="L32" class="LineNr"> 32 </span>    <span class="muControl">break-unless</span> old-recipe-errors
-<span id="L33" class="LineNr"> 33 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L33" class="LineNr"> 33 </span>    <a href='../081print.mu.html#L16'>screen</a> <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L431'>render-recipes</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L34" class="LineNr"> 34 </span>  <span class="Delimiter">}</span>
 <span id="L35" class="LineNr"> 35 </span>  <a href='011-errors.mu.html#L42'>render-recipe-errors</a> env, <a href='../081print.mu.html#L16'>screen</a>
 <span id="L36" class="LineNr"> 36 </span>]
@@ -115,7 +115,7 @@ if ('onhashchange' in window) {
 <span id="L53" class="LineNr"> 53 </span>  <span class="Comment"># draw dotted line after recipes</span>
 <span id="L54" class="LineNr"> 54 </span>  <a href='002-typing.mu.html#L1114'>draw-horizontal</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, right, <span class="Constant">9480/horizontal-dotted</span>
 <span id="L55" class="LineNr"> 55 </span>  row <span class="Special">&lt;-</span> add row,<span class="Constant"> 1</span>
-<span id="L56" class="LineNr"> 56 </span>  <a href='001-editor.mu.html#L209'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
+<span id="L56" class="LineNr"> 56 </span>  <a href='001-editor.mu.html#L211'>clear-screen-from</a> <a href='../081print.mu.html#L16'>screen</a>, row, left, left, right
 <span id="L57" class="LineNr"> 57 </span>]
 <span id="L58" class="LineNr"> 58 </span>
 <span id="L59" class="LineNr"> 59 </span><span class="muData">container</span> environment [
@@ -135,7 +135,7 @@ if ('onhashchange' in window) {
 <span id="L73" class="LineNr"> 73 </span>    error-index:num <span class="Special">&lt;-</span> get *env, <span class="Constant">error-index:offset</span>
 <span id="L74" class="LineNr"> 74 </span>    sandboxes-completed-successfully?:bool <span class="Special">&lt;-</span> equal error-index,<span class="Constant"> -1</span>
 <span id="L75" class="LineNr"> 75 </span>    <span class="muControl">break-if</span> sandboxes-completed-successfully?
-<span id="L76" class="LineNr"> 76 </span>    errors-found? <span class="Special">&lt;-</span> copy <span class="Constant">1/true</span>
+<span id="L76" class="LineNr"> 76 </span>    errors-found? <span class="Special">&lt;-</span> copy<span class="Constant"> true</span>
 <span id="L77" class="LineNr"> 77 </span>  <span class="Delimiter">}</span>
 <span id="L78" class="LineNr"> 78 </span>]
 <span id="L79" class="LineNr"> 79 </span>
@@ -206,7 +206,7 @@ if ('onhashchange' in window) {
 <span id="L144" class="LineNr">144 </span>    ]
 <span id="L145" class="LineNr">145 </span>  ]
 <span id="L146" class="LineNr">146 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L147" class="LineNr">147 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L147" class="LineNr">147 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L148" class="LineNr">148 </span>  screen-should-contain [
 <span id="L149" class="LineNr">149 </span>   <span class="Constant"> .                                                                                 run (F4)           .</span>
 <span id="L150" class="LineNr">150 </span>   <span class="Constant"> .recipe foo [                                      ╎foo                                              .</span>
@@ -254,7 +254,7 @@ if ('onhashchange' in window) {
 <span id="L192" class="LineNr">192 </span>  assume-resources [
 <span id="L193" class="LineNr">193 </span>  ]
 <span id="L194" class="LineNr">194 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>
-<span id="L195" class="LineNr">195 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L195" class="LineNr">195 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L196" class="LineNr">196 </span>  assume-console [
 <span id="L197" class="LineNr">197 </span>    type <span class="Constant">[recipe foo x [</span>
 <span id="L198" class="LineNr">198 </span><span class="Constant">]</span>]
@@ -280,7 +280,7 @@ if ('onhashchange' in window) {
 <span id="L218" class="LineNr">218 </span>  assume-resources [
 <span id="L219" class="LineNr">219 </span>  ]
 <span id="L220" class="LineNr">220 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L221" class="LineNr">221 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L221" class="LineNr">221 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L222" class="LineNr">222 </span>  assume-console [
 <span id="L223" class="LineNr">223 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 80</span>
 <span id="L224" class="LineNr">224 </span>    <span class="Comment"># create invalid sandbox 1</span>
@@ -306,7 +306,7 @@ if ('onhashchange' in window) {
 <span id="L244" class="LineNr">244 </span>  assume-resources [
 <span id="L245" class="LineNr">245 </span>  ]
 <span id="L246" class="LineNr">246 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[]</span>
-<span id="L247" class="LineNr">247 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L247" class="LineNr">247 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L248" class="LineNr">248 </span>  assume-console [
 <span id="L249" class="LineNr">249 </span>    left-click<span class="Constant"> 3</span>,<span class="Constant"> 80</span>
 <span id="L250" class="LineNr">250 </span>    <span class="Comment"># create invalid sandbox 2</span>
@@ -335,7 +335,7 @@ if ('onhashchange' in window) {
 <span id="L273" class="LineNr">273 </span>  assume-resources [
 <span id="L274" class="LineNr">274 </span>  ]
 <span id="L275" class="LineNr">275 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[get foo, x:offset]</span>  <span class="Comment"># invalid</span>
-<span id="L276" class="LineNr">276 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L276" class="LineNr">276 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L277" class="LineNr">277 </span>  assume-console [
 <span id="L278" class="LineNr">278 </span>    press F4  <span class="Comment"># generate error</span>
 <span id="L279" class="LineNr">279 </span>  ]
@@ -372,13 +372,13 @@ if ('onhashchange' in window) {
 <span id="L310" class="LineNr">310 </span>      <span class="Constant">|recipe</span> foo x:_elem<span class="muRecipe"> -&gt; </span>z:_elem <span class="Constant">[|</span>
 <span id="L311" class="LineNr">311 </span><span class="Constant">      |  local-scope|</span>
 <span id="L312" class="LineNr">312 </span><span class="Constant">      |  load-ingredients|</span>
-<span id="L313" class="LineNr">313 </span><span class="Constant">      |  y:&amp;:num &lt;- copy 0|</span>
+<span id="L313" class="LineNr">313 </span><span class="Constant">      |  y:&amp;:num &lt;- copy null|</span>
 <span id="L314" class="LineNr">314 </span><span class="Constant">      |  z &lt;- add x, y|</span>
 <span id="L315" class="LineNr">315 </span><span class="Constant">      |]</span>|
 <span id="L316" class="LineNr">316 </span>    ]
 <span id="L317" class="LineNr">317 </span>  ]
 <span id="L318" class="LineNr">318 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo 2]</span>
-<span id="L319" class="LineNr">319 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L319" class="LineNr">319 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L320" class="LineNr">320 </span>  assume-console [
 <span id="L321" class="LineNr">321 </span>    press F4
 <span id="L322" class="LineNr">322 </span>  ]
@@ -388,7 +388,7 @@ if ('onhashchange' in window) {
 <span id="L326" class="LineNr">326 </span>   <span class="Constant"> .recipe foo x:_elem -&gt; z:_elem [                   ╎                                                 .</span>
 <span id="L327" class="LineNr">327 </span>   <span class="Constant"> .  local-scope                                     ╎─────────────────────────────────────────────────.</span>
 <span id="L328" class="LineNr">328 </span>   <span class="Constant"> .  load-ingredients                                ╎0   edit       copy       to recipe    delete    .</span>
-<span id="L329" class="LineNr">329 </span>   <span class="Constant"> .  y:&amp;:num &lt;- copy 0                               ╎foo 2                                            .</span>
+<span id="L329" class="LineNr">329 </span>   <span class="Constant"> .  y:&amp;:num &lt;- copy null                            ╎foo 2                                            .</span>
 <span id="L330" class="LineNr">330 </span>   <span class="Constant"> .  z &lt;- add x, y                                   ╎foo_2: 'add' requires number ingredients, but go↩.</span>
 <span id="L331" class="LineNr">331 </span>   <span class="Constant"> .]                                                 ╎t 'y'                                            .</span>
 <span id="L332" class="LineNr">332 </span>   <span class="Constant"> .                                                  ╎─────────────────────────────────────────────────.</span>
@@ -408,7 +408,7 @@ if ('onhashchange' in window) {
 <span id="L346" class="LineNr">346 </span>   <span class="Constant"> .recipe foo x:_elem -&gt; z:_elem [                   ╎                                                 .</span>
 <span id="L347" class="LineNr">347 </span>   <span class="Constant"> .  local-scope                                     ╎─────────────────────────────────────────────────.</span>
 <span id="L348" class="LineNr">348 </span>   <span class="Constant"> .  load-ingredients                                ╎0   edit       copy       to recipe    delete    .</span>
-<span id="L349" class="LineNr">349 </span>   <span class="Constant"> .  y:&amp;:num &lt;- copy 0                               ╎foo 2                                            .</span>
+<span id="L349" class="LineNr">349 </span>   <span class="Constant"> .  y:&amp;:num &lt;- copy null                            ╎foo 2                                            .</span>
 <span id="L350" class="LineNr">350 </span>   <span class="Constant"> .  z &lt;- add x, y                                   ╎foo_3: 'add' requires number ingredients, but go↩.</span>
 <span id="L351" class="LineNr">351 </span>   <span class="Constant"> .]                                                 ╎t 'y'                                            .</span>
 <span id="L352" class="LineNr">352 </span>   <span class="Constant"> .                                                  ╎─────────────────────────────────────────────────.</span>
@@ -429,10 +429,10 @@ if ('onhashchange' in window) {
 <span id="L367" class="LineNr">367 </span>    ]
 <span id="L368" class="LineNr">368 </span>  ]
 <span id="L369" class="LineNr">369 </span>  <span class="Comment"># call code that uses other variants of it, but not it itself</span>
-<span id="L370" class="LineNr">370 </span>  test-sandbox:text <span class="Special">&lt;-</span> new <span class="Constant">[x:&amp;:<a href='../064list.mu.html#L6'>list</a>:num &lt;- copy 0</span>
+<span id="L370" class="LineNr">370 </span>  test-sandbox:text <span class="Special">&lt;-</span> new <span class="Constant">[x:&amp;:<a href='../064list.mu.html#L6'>list</a>:num &lt;- copy null</span>
 <span id="L371" class="LineNr">371 </span><span class="Constant">to-text x]</span>
 <span id="L372" class="LineNr">372 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, test-sandbox
-<span id="L373" class="LineNr">373 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L373" class="LineNr">373 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L374" class="LineNr">374 </span>  <span class="Comment"># run it once</span>
 <span id="L375" class="LineNr">375 </span>  assume-console [
 <span id="L376" class="LineNr">376 </span>    press F4
@@ -495,7 +495,7 @@ if ('onhashchange' in window) {
 <span id="L433" class="LineNr">433 </span>    ]
 <span id="L434" class="LineNr">434 </span>  ]
 <span id="L435" class="LineNr">435 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L436" class="LineNr">436 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L436" class="LineNr">436 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L437" class="LineNr">437 </span>  assume-console [
 <span id="L438" class="LineNr">438 </span>    press F4
 <span id="L439" class="LineNr">439 </span>  ]
@@ -509,7 +509,7 @@ if ('onhashchange' in window) {
 <span id="L447" class="LineNr">447 </span>   <span class="Constant"> .]                                                 ╎                                                 .</span>
 <span id="L448" class="LineNr">448 </span>   <span class="Constant"> .                                                  ╎                                                 .</span>
 <span id="L449" class="LineNr">449 </span>   <span class="Constant"> .foo: missing type for 'x' in 'x &lt;- copy 0'        ╎                                                 .</span>
-<span id="L450" class="LineNr">450 </span>   <span class="Constant"> .foo: can't copy '0' to 'x'; types don't <a href='../065duplex_list.mu.html#L585'>match</a>     ╎                                                 .</span>
+<span id="L450" class="LineNr">450 </span>   <span class="Constant"> .foo: can't copy '0' to 'x'; types don't <a href='../065duplex_list.mu.html#L642'>match</a>     ╎                                                 .</span>
 <span id="L451" class="LineNr">451 </span>   <span class="Constant"> .╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╎                                                 .</span>
 <span id="L452" class="LineNr">452 </span>   <span class="Constant"> .                                                  ╎                                                 .</span>
 <span id="L453" class="LineNr">453 </span>  ]
@@ -527,7 +527,7 @@ if ('onhashchange' in window) {
 <span id="L465" class="LineNr">465 </span><span class="Constant">    ]</span>
 <span id="L466" class="LineNr">466 </span>  ]
 <span id="L467" class="LineNr">467 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L468" class="LineNr">468 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L468" class="LineNr">468 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L469" class="LineNr">469 </span>  assume-console [
 <span id="L470" class="LineNr">470 </span>    press F4
 <span id="L471" class="LineNr">471 </span>  ]
@@ -559,7 +559,7 @@ if ('onhashchange' in window) {
 <span id="L497" class="LineNr">497 </span>    ]
 <span id="L498" class="LineNr">498 </span>  ]
 <span id="L499" class="LineNr">499 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L500" class="LineNr">500 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L500" class="LineNr">500 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L501" class="LineNr">501 </span>  assume-console [
 <span id="L502" class="LineNr">502 </span>    press F4
 <span id="L503" class="LineNr">503 </span>  ]
@@ -596,7 +596,7 @@ if ('onhashchange' in window) {
 <span id="L534" class="LineNr">534 </span>    ]
 <span id="L535" class="LineNr">535 </span>  ]
 <span id="L536" class="LineNr">536 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L537" class="LineNr">537 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L537" class="LineNr">537 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L538" class="LineNr">538 </span>  assume-console [
 <span id="L539" class="LineNr">539 </span>    press F4
 <span id="L540" class="LineNr">540 </span>  ]
@@ -633,7 +633,7 @@ if ('onhashchange' in window) {
 <span id="L571" class="LineNr">571 </span>    ]
 <span id="L572" class="LineNr">572 </span>  ]
 <span id="L573" class="LineNr">573 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L574" class="LineNr">574 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L574" class="LineNr">574 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L575" class="LineNr">575 </span>  assume-console [
 <span id="L576" class="LineNr">576 </span>    press F4
 <span id="L577" class="LineNr">577 </span>  ]
@@ -685,7 +685,7 @@ if ('onhashchange' in window) {
 <span id="L623" class="LineNr">623 </span>    ]
 <span id="L624" class="LineNr">624 </span>  ]
 <span id="L625" class="LineNr">625 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L626" class="LineNr">626 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L626" class="LineNr">626 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L627" class="LineNr">627 </span>  assume-console [
 <span id="L628" class="LineNr">628 </span>    press F4
 <span id="L629" class="LineNr">629 </span>  ]
@@ -738,11 +738,11 @@ if ('onhashchange' in window) {
 <span id="L676" class="LineNr">676 </span>    ]
 <span id="L677" class="LineNr">677 </span>  ]
 <span id="L678" class="LineNr">678 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L679" class="LineNr">679 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L679" class="LineNr">679 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L680" class="LineNr">680 </span>  <span class="Comment"># hit F4, generating errors, then scroll down</span>
 <span id="L681" class="LineNr">681 </span>  assume-console [
 <span id="L682" class="LineNr">682 </span>    press F4
-<span id="L683" class="LineNr">683 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L683" class="LineNr">683 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L684" class="LineNr">684 </span>  ]
 <span id="L685" class="LineNr">685 </span>  run [
 <span id="L686" class="LineNr">686 </span>    <a href='004-programming-environment.mu.html#L39'>event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, env, <a href='../088file.mu.html#L11'>resources</a>
@@ -765,7 +765,7 @@ if ('onhashchange' in window) {
 <span id="L703" class="LineNr">703 </span>  ]
 <span id="L704" class="LineNr">704 </span>  <span class="Comment"># sandbox editor contains an illegal instruction</span>
 <span id="L705" class="LineNr">705 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[get 1234:num, foo:offset]</span>
-<span id="L706" class="LineNr">706 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L706" class="LineNr">706 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L707" class="LineNr">707 </span>  assume-console [
 <span id="L708" class="LineNr">708 </span>    press F4
 <span id="L709" class="LineNr">709 </span>  ]
@@ -828,7 +828,7 @@ if ('onhashchange' in window) {
 <span id="L766" class="LineNr">766 </span>  ]
 <span id="L767" class="LineNr">767 </span>  <span class="Comment"># sandbox editor contains an illegal instruction</span>
 <span id="L768" class="LineNr">768 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[get 1234:num, foo:offset]</span>
-<span id="L769" class="LineNr">769 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L769" class="LineNr">769 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L770" class="LineNr">770 </span>  <span class="Comment"># run the code in the editors multiple times</span>
 <span id="L771" class="LineNr">771 </span>  assume-console [
 <span id="L772" class="LineNr">772 </span>    press F4
@@ -867,7 +867,7 @@ if ('onhashchange' in window) {
 <span id="L805" class="LineNr">805 </span>    ]
 <span id="L806" class="LineNr">806 </span>  ]
 <span id="L807" class="LineNr">807 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo]</span>
-<span id="L808" class="LineNr">808 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L808" class="LineNr">808 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L809" class="LineNr">809 </span>  <span class="Comment"># run the sandbox</span>
 <span id="L810" class="LineNr">810 </span>  assume-console [
 <span id="L811" class="LineNr">811 </span>    press F4
@@ -906,7 +906,7 @@ if ('onhashchange' in window) {
 <span id="L844" class="LineNr">844 </span>    ]
 <span id="L845" class="LineNr">845 </span>  ]
 <span id="L846" class="LineNr">846 </span>  env:&amp;:environment <span class="Special">&lt;-</span> <a href='004-programming-environment.mu.html#L21'>new-programming-environment</a> <a href='../088file.mu.html#L11'>resources</a>, <a href='../081print.mu.html#L16'>screen</a>, <span class="Constant">[foo 4, 0]</span>
-<span id="L847" class="LineNr">847 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L107'>render</a>
+<span id="L847" class="LineNr">847 </span>  <a href='004-programming-environment.mu.html#L402'>render-all</a> <a href='../081print.mu.html#L16'>screen</a>, env, <a href='001-editor.mu.html#L109'>render</a>
 <span id="L848" class="LineNr">848 </span>  <span class="Comment"># run</span>
 <span id="L849" class="LineNr">849 </span>  assume-console [
 <span id="L850" class="LineNr">850 </span>    press F4
diff --git a/html/edit/012-editor-undo.mu.html b/html/edit/012-editor-undo.mu.html
index ca822068..705a47e4 100644
--- a/html/edit/012-editor-undo.mu.html
+++ b/html/edit/012-editor-undo.mu.html
@@ -15,17 +15,17 @@ body { font-size: 12pt; font-family: monospace; color: #aaaaaa; background-color
 a { color:#eeeeee; text-decoration: none; }
 a:hover { text-decoration: underline; }
 * { font-size: 12pt; font-size: 1em; }
+.muData { color: #ffff00; }
 .muRecipe { color: #ff8700; }
-.muScenario { color: #00af00; }
 .Special { color: #c00000; }
 .Delimiter { color: #800080; }
 .SalientComment { color: #00ffff; }
 .Constant { color: #00a0a0; }
 .LineNr { color: #444444; }
+.muControl { color: #c0a020; }
 .Comment { color: #9090ff; }
 .Comment a { color:#0000ee; text-decoration:underline; }
-.muControl { color: #c0a020; }
-.muData { color: #ffff00; }
+.muScenario { color: #00af00; }
 -->
 </style>
 
@@ -138,7 +138,7 @@ if ('onhashchange' in window) {
 <span id="L76" class="LineNr">  76 </span>    redo <span class="Special">&lt;-</span> push op, redo
 <span id="L77" class="LineNr">  77 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">redo:offset</span>, redo
 <span id="L78" class="LineNr">  78 </span><span class="Constant">    <a href='012-editor-undo.mu.html#L78'>&lt;handle-undo&gt;</a></span>
-<span id="L79" class="LineNr">  79 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L79" class="LineNr">  79 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L80" class="LineNr">  80 </span>  <span class="Delimiter">}</span>
 <span id="L81" class="LineNr">  81 </span>]
 <span id="L82" class="LineNr">  82 </span>
@@ -156,7 +156,7 @@ if ('onhashchange' in window) {
 <span id="L94" class="LineNr">  94 </span>    undo <span class="Special">&lt;-</span> push op, undo
 <span id="L95" class="LineNr">  95 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">undo:offset</span>, undo
 <span id="L96" class="LineNr">  96 </span><span class="Constant">    <a href='012-editor-undo.mu.html#L96'>&lt;handle-redo&gt;</a></span>
-<span id="L97" class="LineNr">  97 </span>   <span class="muControl"> return</span> <span class="Constant">1/go-render</span>
+<span id="L97" class="LineNr">  97 </span>   <span class="muControl"> return</span><span class="Constant"> true/go-render</span>
 <span id="L98" class="LineNr">  98 </span>  <span class="Delimiter">}</span>
 <span id="L99" class="LineNr">  99 </span>]
 <span id="L100" class="LineNr"> 100 </span>
@@ -220,7 +220,7 @@ if ('onhashchange' in window) {
 <span id="L158" class="LineNr"> 158 </span>    previous-coalesce-tag:num <span class="Special">&lt;-</span> get typing, <span class="Constant">tag:offset</span>
 <span id="L159" class="LineNr"> 159 </span>    <span class="muControl">break-unless</span> previous-coalesce-tag
 <span id="L160" class="LineNr"> 160 </span>    before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L161" class="LineNr"> 161 </span>    insert-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L161" class="LineNr"> 161 </span>    insert-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L162" class="LineNr"> 162 </span>    typing <span class="Special">&lt;-</span> put typing, <span class="Constant">insert-until:offset</span>, insert-until
 <span id="L163" class="LineNr"> 163 </span>    typing <span class="Special">&lt;-</span> put typing, <span class="Constant">after-row:offset</span>, cursor-row
 <span id="L164" class="LineNr"> 164 </span>    typing <span class="Special">&lt;-</span> put typing, <span class="Constant">after-column:offset</span>, cursor-column
@@ -229,8 +229,8 @@ if ('onhashchange' in window) {
 <span id="L167" class="LineNr"> 167 </span>   <span class="muControl"> break</span> <span class="Constant">+done-adding-insert-operation</span>
 <span id="L168" class="LineNr"> 168 </span>  <span class="Delimiter">}</span>
 <span id="L169" class="LineNr"> 169 </span>  <span class="Comment"># if not, create a new operation</span>
-<span id="L170" class="LineNr"> 170 </span>  insert-from:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> cursor-before
-<span id="L171" class="LineNr"> 171 </span>  insert-to:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> insert-from
+<span id="L170" class="LineNr"> 170 </span>  insert-from:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> cursor-before
+<span id="L171" class="LineNr"> 171 </span>  insert-to:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> insert-from
 <span id="L172" class="LineNr"> 172 </span>  op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
 <span id="L173" class="LineNr"> 173 </span>  *op <span class="Special">&lt;-</span> merge <span class="Constant">0/insert-operation</span>, save-row/before, save-column/before, top-before, cursor-row/after, cursor-column/after, top-after, insert-from, insert-to, <span class="Constant">1/coalesce</span>
 <span id="L174" class="LineNr"> 174 </span>  editor <span class="Special">&lt;-</span> <a href='012-editor-undo.mu.html#L202'>add-operation</a> editor, op
@@ -249,9 +249,9 @@ if ('onhashchange' in window) {
 <span id="L187" class="LineNr"> 187 </span>  cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L188" class="LineNr"> 188 </span>  cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L189" class="LineNr"> 189 </span>  <span class="Comment"># never coalesce</span>
-<span id="L190" class="LineNr"> 190 </span>  insert-from:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> cursor-before
+<span id="L190" class="LineNr"> 190 </span>  insert-from:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> cursor-before
 <span id="L191" class="LineNr"> 191 </span>  before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L192" class="LineNr"> 192 </span>  insert-to:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L192" class="LineNr"> 192 </span>  insert-to:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L193" class="LineNr"> 193 </span>  op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
 <span id="L194" class="LineNr"> 194 </span>  *op <span class="Special">&lt;-</span> merge <span class="Constant">0/insert-operation</span>, cursor-row-before, cursor-column-before, top-before, cursor-row/after, cursor-column/after, top-after, insert-from, insert-to, <span class="Constant">0/never-coalesce</span>
 <span id="L195" class="LineNr"> 195 </span>  editor <span class="Special">&lt;-</span> <a href='012-editor-undo.mu.html#L202'>add-operation</a> editor, op
@@ -268,7 +268,7 @@ if ('onhashchange' in window) {
 <span id="L206" class="LineNr"> 206 </span>  undo <span class="Special">&lt;-</span> push op undo
 <span id="L207" class="LineNr"> 207 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">undo:offset</span>, undo
 <span id="L208" class="LineNr"> 208 </span>  redo:&amp;:<a href='../064list.mu.html#L6'>list</a>:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> get *editor, <span class="Constant">redo:offset</span>
-<span id="L209" class="LineNr"> 209 </span>  redo <span class="Special">&lt;-</span> copy<span class="Constant"> 0</span>
+<span id="L209" class="LineNr"> 209 </span>  redo <span class="Special">&lt;-</span> copy<span class="Constant"> null</span>
 <span id="L210" class="LineNr"> 210 </span>  *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">redo:offset</span>, redo
 <span id="L211" class="LineNr"> 211 </span>]
 <span id="L212" class="LineNr"> 212 </span>
@@ -279,9 +279,9 @@ if ('onhashchange' in window) {
 <span id="L217" class="LineNr"> 217 </span>    start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get typing, <span class="Constant">insert-from:offset</span>
 <span id="L218" class="LineNr"> 218 </span>    end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get typing, <span class="Constant">insert-until:offset</span>
 <span id="L219" class="LineNr"> 219 </span>    <span class="Comment"># assert cursor-row/cursor-column/top-of-screen match after-row/after-column/after-top-of-screen</span>
-<span id="L220" class="LineNr"> 220 </span>    before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L32'>prev</a> start
+<span id="L220" class="LineNr"> 220 </span>    before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L38'>prev</a> start
 <span id="L221" class="LineNr"> 221 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">before-cursor:offset</span>, before-cursor
-<span id="L222" class="LineNr"> 222 </span>    <a href='../065duplex_list.mu.html#L385'>remove-between</a> before-cursor, end
+<span id="L222" class="LineNr"> 222 </span>    <a href='../065duplex_list.mu.html#L391'>remove-between</a> before-cursor, end
 <span id="L223" class="LineNr"> 223 </span>    cursor-row <span class="Special">&lt;-</span> get typing, <span class="Constant">before-row:offset</span>
 <span id="L224" class="LineNr"> 224 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
 <span id="L225" class="LineNr"> 225 </span>    cursor-column <span class="Special">&lt;-</span> get typing, <span class="Constant">before-column:offset</span>
@@ -479,7 +479,7 @@ if ('onhashchange' in window) {
 <span id="L417" class="LineNr"> 417 </span>    before-cursor <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
 <span id="L418" class="LineNr"> 418 </span>    insert-from:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get typing, <span class="Constant">insert-from:offset</span>  <span class="Comment"># ignore insert-to because it's already been spliced away</span>
 <span id="L419" class="LineNr"> 419 </span>    <span class="Comment"># assert insert-to matches next(before-cursor)</span>
-<span id="L420" class="LineNr"> 420 </span>    <a href='../065duplex_list.mu.html#L525'>splice</a> before-cursor, insert-from
+<span id="L420" class="LineNr"> 420 </span>    <a href='../065duplex_list.mu.html#L582'>splice</a> before-cursor, insert-from
 <span id="L421" class="LineNr"> 421 </span>    <span class="Comment"># assert cursor-row/cursor-column/top-of-screen match after-row/after-column/after-top-of-screen</span>
 <span id="L422" class="LineNr"> 422 </span>    cursor-row <span class="Special">&lt;-</span> get typing, <span class="Constant">after-row:offset</span>
 <span id="L423" class="LineNr"> 423 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
@@ -1080,7 +1080,7 @@ if ('onhashchange' in window) {
 <span id="L1018" class="LineNr">1018 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L1019" class="LineNr">1019 </span>  <span class="Comment"># scroll the page</span>
 <span id="L1020" class="LineNr">1020 </span>  assume-console [
-<span id="L1021" class="LineNr">1021 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1021" class="LineNr">1021 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1022" class="LineNr">1022 </span>  ]
 <span id="L1023" class="LineNr">1023 </span>  <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L1024" class="LineNr">1024 </span>  <span class="Comment"># undo</span>
@@ -1114,7 +1114,7 @@ if ('onhashchange' in window) {
 <span id="L1052" class="LineNr">1052 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L1053" class="LineNr">1053 </span>  <span class="Comment"># scroll the page down and up</span>
 <span id="L1054" class="LineNr">1054 </span>  assume-console [
-<span id="L1055" class="LineNr">1055 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
+<span id="L1055" class="LineNr">1055 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
 <span id="L1056" class="LineNr">1056 </span>    press ctrl-b
 <span id="L1057" class="LineNr">1057 </span>  ]
 <span id="L1058" class="LineNr">1058 </span>  <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
@@ -1149,8 +1149,8 @@ if ('onhashchange' in window) {
 <span id="L1087" class="LineNr">1087 </span>  <a href='002-typing.mu.html#L265'>editor-render</a> <a href='../081print.mu.html#L16'>screen</a>, e
 <span id="L1088" class="LineNr">1088 </span>  <span class="Comment"># scroll the page down and up</span>
 <span id="L1089" class="LineNr">1089 </span>  assume-console [
-<span id="L1090" class="LineNr">1090 </span>    press <a href='003-shortcuts.mu.html#L3597'>page-down</a>
-<span id="L1091" class="LineNr">1091 </span>    press <a href='003-shortcuts.mu.html#L3820'>page-up</a>
+<span id="L1090" class="LineNr">1090 </span>    press <a href='003-shortcuts.mu.html#L3610'>page-down</a>
+<span id="L1091" class="LineNr">1091 </span>    press <a href='003-shortcuts.mu.html#L3833'>page-up</a>
 <span id="L1092" class="LineNr">1092 </span>  ]
 <span id="L1093" class="LineNr">1093 </span>  <a href='002-typing.mu.html#L16'>editor-event-loop</a> <a href='../081print.mu.html#L16'>screen</a>, <a href='../084console.mu.html#L23'>console</a>, e
 <span id="L1094" class="LineNr">1094 </span>  <span class="Comment"># undo</span>
@@ -1700,7 +1700,7 @@ if ('onhashchange' in window) {
 <span id="L1638" class="LineNr">1638 </span>      <span class="muControl">break-unless</span> coalesce?
 <span id="L1639" class="LineNr">1639 </span>      deletion <span class="Special">&lt;-</span> put deletion, <span class="Constant">delete-from:offset</span>, before-cursor
 <span id="L1640" class="LineNr">1640 </span>      backspaced-so-far:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">deleted-text:offset</span>
-<span id="L1641" class="LineNr">1641 </span>      <a href='../065duplex_list.mu.html#L525'>splice</a> backspaced-cell, backspaced-so-far
+<span id="L1641" class="LineNr">1641 </span>      <a href='../065duplex_list.mu.html#L582'>splice</a> backspaced-cell, backspaced-so-far
 <span id="L1642" class="LineNr">1642 </span>      deletion <span class="Special">&lt;-</span> put deletion, <span class="Constant">deleted-text:offset</span>, backspaced-cell
 <span id="L1643" class="LineNr">1643 </span>      deletion <span class="Special">&lt;-</span> put deletion, <span class="Constant">after-row:offset</span>, cursor-row
 <span id="L1644" class="LineNr">1644 </span>      deletion <span class="Special">&lt;-</span> put deletion, <span class="Constant">after-column:offset</span>, cursor-column
@@ -1710,7 +1710,7 @@ if ('onhashchange' in window) {
 <span id="L1648" class="LineNr">1648 </span>    <span class="Delimiter">}</span>
 <span id="L1649" class="LineNr">1649 </span>    <span class="Comment"># if not, create a new operation</span>
 <span id="L1650" class="LineNr">1650 </span>    op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
-<span id="L1651" class="LineNr">1651 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1651" class="LineNr">1651 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1652" class="LineNr">1652 </span>    *op <span class="Special">&lt;-</span> merge <span class="Constant">2/delete-operation</span>, save-row/before, save-column/before, top-before, cursor-row/after, cursor-column/after, top-after, backspaced-cell/deleted, before-cursor/delete-from, deleted-until, <span class="Constant">1/coalesce-backspace</span>
 <span id="L1653" class="LineNr">1653 </span>    editor <span class="Special">&lt;-</span> <a href='012-editor-undo.mu.html#L202'>add-operation</a> editor, op
 <span id="L1654" class="LineNr">1654 </span><span class="Constant">    +done-adding-backspace-operation</span>
@@ -1724,8 +1724,8 @@ if ('onhashchange' in window) {
 <span id="L1662" class="LineNr">1662 </span>    anchor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">delete-from:offset</span>
 <span id="L1663" class="LineNr">1663 </span>    <span class="muControl">break-unless</span> anchor
 <span id="L1664" class="LineNr">1664 </span>    deleted:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">deleted-text:offset</span>
-<span id="L1665" class="LineNr">1665 </span>    old-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L572'>last</a> deleted
-<span id="L1666" class="LineNr">1666 </span>    <a href='../065duplex_list.mu.html#L525'>splice</a> anchor, deleted
+<span id="L1665" class="LineNr">1665 </span>    old-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L629'>last</a> deleted
+<span id="L1666" class="LineNr">1666 </span>    <a href='../065duplex_list.mu.html#L582'>splice</a> anchor, deleted
 <span id="L1667" class="LineNr">1667 </span>    <span class="Comment"># assert cursor-row/cursor-column/top-of-screen match after-row/after-column/after-top-of-screen</span>
 <span id="L1668" class="LineNr">1668 </span>    before-cursor <span class="Special">&lt;-</span> copy old-cursor
 <span id="L1669" class="LineNr">1669 </span>    cursor-row <span class="Special">&lt;-</span> get deletion, <span class="Constant">before-row:offset</span>
@@ -1744,7 +1744,7 @@ if ('onhashchange' in window) {
 <span id="L1682" class="LineNr">1682 </span>    start:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">delete-from:offset</span>
 <span id="L1683" class="LineNr">1683 </span>    end:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">delete-until:offset</span>
 <span id="L1684" class="LineNr">1684 </span>    data:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">data:offset</span>
-<span id="L1685" class="LineNr">1685 </span>    <a href='../065duplex_list.mu.html#L385'>remove-between</a> start, end
+<span id="L1685" class="LineNr">1685 </span>    <a href='../065duplex_list.mu.html#L391'>remove-between</a> start, end
 <span id="L1686" class="LineNr">1686 </span>    <span class="Comment"># assert cursor-row/cursor-column/top-of-screen match after-row/after-column/after-top-of-screen</span>
 <span id="L1687" class="LineNr">1687 </span>    cursor-row <span class="Special">&lt;-</span> get deletion, <span class="Constant">after-row:offset</span>
 <span id="L1688" class="LineNr">1688 </span>    *editor <span class="Special">&lt;-</span> put *editor, <span class="Constant">cursor-row:offset</span>, cursor-row
@@ -1924,7 +1924,7 @@ if ('onhashchange' in window) {
 <span id="L1862" class="LineNr">1862 </span>      previous-coalesce-tag:num <span class="Special">&lt;-</span> get deletion, <span class="Constant">tag:offset</span>
 <span id="L1863" class="LineNr">1863 </span>      coalesce?:bool <span class="Special">&lt;-</span> equal previous-coalesce-tag, <span class="Constant">2/coalesce-delete</span>
 <span id="L1864" class="LineNr">1864 </span>      <span class="muControl">break-unless</span> coalesce?
-<span id="L1865" class="LineNr">1865 </span>      delete-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1865" class="LineNr">1865 </span>      delete-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1866" class="LineNr">1866 </span>      deletion <span class="Special">&lt;-</span> put deletion, <span class="Constant">delete-until:offset</span>, delete-until
 <span id="L1867" class="LineNr">1867 </span>      deleted-so-far:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get deletion, <span class="Constant">deleted-text:offset</span>
 <span id="L1868" class="LineNr">1868 </span>      deleted-so-far <span class="Special">&lt;-</span> append deleted-so-far, deleted-cell
@@ -1937,7 +1937,7 @@ if ('onhashchange' in window) {
 <span id="L1875" class="LineNr">1875 </span>    <span class="Delimiter">}</span>
 <span id="L1876" class="LineNr">1876 </span>    <span class="Comment"># if not, create a new operation</span>
 <span id="L1877" class="LineNr">1877 </span>    op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
-<span id="L1878" class="LineNr">1878 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1878" class="LineNr">1878 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1879" class="LineNr">1879 </span>    *op <span class="Special">&lt;-</span> merge <span class="Constant">2/delete-operation</span>, save-row/before, save-column/before, top-before, cursor-row/after, cursor-column/after, top-after, deleted-cell/deleted, before-cursor/delete-from, deleted-until, <span class="Constant">2/coalesce-delete</span>
 <span id="L1880" class="LineNr">1880 </span>    editor <span class="Special">&lt;-</span> <a href='012-editor-undo.mu.html#L202'>add-operation</a> editor, op
 <span id="L1881" class="LineNr">1881 </span><span class="Constant">    +done-adding-delete-operation</span>
@@ -2039,7 +2039,7 @@ if ('onhashchange' in window) {
 <span id="L1977" class="LineNr">1977 </span>    top-after:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
 <span id="L1978" class="LineNr">1978 </span>    cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L1979" class="LineNr">1979 </span>    cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
-<span id="L1980" class="LineNr">1980 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L1980" class="LineNr">1980 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L1981" class="LineNr">1981 </span>    op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
 <span id="L1982" class="LineNr">1982 </span>    *op <span class="Special">&lt;-</span> merge <span class="Constant">2/delete-operation</span>, save-row/before, save-column/before, top-before, cursor-row/after, cursor-column/after, top-after, deleted-cells/deleted, before-cursor/delete-from, deleted-until, <span class="Constant">0/never-coalesce</span>
 <span id="L1983" class="LineNr">1983 </span>    editor <span class="Special">&lt;-</span> <a href='012-editor-undo.mu.html#L202'>add-operation</a> editor, op
@@ -2142,7 +2142,7 @@ if ('onhashchange' in window) {
 <span id="L2080" class="LineNr">2080 </span>    top-after:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">top-of-screen:offset</span>
 <span id="L2081" class="LineNr">2081 </span>    op:&amp;:<a href='012-editor-undo.mu.html#L5'>operation</a> <span class="Special">&lt;-</span> new <span class="Constant"><a href='012-editor-undo.mu.html#L5'>operation</a>:type</span>
 <span id="L2082" class="LineNr">2082 </span>    before-cursor:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> get *editor, <span class="Constant">before-cursor:offset</span>
-<span id="L2083" class="LineNr">2083 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L25'>next</a> before-cursor
+<span id="L2083" class="LineNr">2083 </span>    deleted-until:&amp;:<a href='../065duplex_list.mu.html#L3'>duplex-list</a>:char <span class="Special">&lt;-</span> <a href='../065duplex_list.mu.html#L31'>next</a> before-cursor
 <span id="L2084" class="LineNr">2084 </span>    cursor-row:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-row:offset</span>
 <span id="L2085" class="LineNr">2085 </span>    cursor-column:num <span class="Special">&lt;-</span> get *editor, <span class="Constant">cursor-column:offset</span>
 <span id="L2086" class="LineNr">2086 </span>    *op <span class="Special">&lt;-</span> merge <span class="Constant">2/delete-operation</span>, save-row/before, save-column/before, top-before, cursor-row/after, cursor-column/after, top-after, deleted-cells/deleted, before-cursor/delete-from, deleted-until, <span class="Constant">0/never-coalesce</span>