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1 files changed, 2 insertions, 1 deletions

diff --git a/Readme.md b/Readme.md
index 94200d0b..27d198e6 100644
--- a/Readme.md
+++ b/Readme.md
@@ -17,7 +17,8 @@ In this quest, Mu is currently experimenting with the following mechanisms:
    screen explicitly takes a screen object, so it can be called on the real
    screen, or on a fake inside tests, so that we can then check the expected
    state of the screen at the end of a test. For example, here's a test for a
-   little text-mode chessboard program in Mu:
+   little text-mode chessboard program in Mu (delimiting the edge of the
+   'screen' with periods):
    <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<img alt='a screen test' src='html/chessboard-test.png'>
    <br>We're building up similarly *dependency-injected* interfaces to the
    keyboard, mouse, touch screen, disk, network, &hellip;