clearer copy

Dependencies

• [2] 66X36NZN a little more prose describing manual_tests
• [3] 4AXV2HG4 all pending manual tests done!
• [*] BJ5X5O4A let's prevent the text cursor from ever getting on a drawing

Change contents

• replacement in Manual_tests.md at line 11
  [2.379]→[2.379:520](∅→∅)
  − byte offsets as _offset, and character positions as _pos. For example,

  − string.sub should never use a _pos to substring, only an _offset.
  [2.379]
  + byte offsets with the suffix `_offset`, and character positions as `_pos`.

  + For example, `string.sub` should never use a `_pos` to substring, only an

  + `_offset`.