current_drawing_mode=Drawing_mode,
    previous_drawing_mode=State.previous_drawing_mode,

      -- invalidate various cached bits of lines
      State.lines.current_drawing = nil

      -- invalidate various cached bits of lines
      State.lines.current_drawing = nil

For shortcuts while editing drawings, consult the online help. Either:
* hover on a drawing and hit `ctrl+h`, or
* click on a drawing to start a stroke and then press and hold `h` to see your
  options at any point during a stroke.

* The text cursor will always stay on the screen. This can have some strange
  implications:
    * A long series of drawings will get silently skipped when you hit
      page-down, until a line of text can be showed on screen.
    * If there's no line of text at the top of the file, you may not be able
      to scroll back up to the top with page-up.
  So far this app isn't really designed for drawing-heavy files. For now I'm
  targeting mostly-text files with a few drawings mixed in.
* No clipping yet for drawings. In particular, circles/squares/rectangles and
  point labels can overflow a drawing.