I care a lot about being able to automatically check _any_ property about my
program before it ever runs. However, some things don't have tests yet, either
because I don't know how to test them or because I've been lazy. I'll at least
record those here.

### Compromises

Lua is dynamically typed. Tests can't patch over lack of type-checking.

* All strings are UTF-8. Bytes within them are not characters. I try to label
  byte offsets as _offset, and character positions as _pos. For example,
  string.sub should never use a _pos to substring, only an _offset.

### Todo list

* resize:
  * Create a file containing a long line of characters without spaces. Try
    resizing the window vertically and horizontally, as far as possible.

* line-width button
  * Create a file containing a single line with a reasonable number of
    characters. Move the cursor towards the end of the line. Click on
    line-width icon in the top margin, slide it left and right. Watch the line
    of characters wrap and unwrap in response. Text should not be selected.