These are great suggestions. I have updated the file to reflect them
as much as I managed to.
I have moved the discussion of the canvas and the possible graphical
systems into the "specification" section and updated the
(canvas-refresh) explanation to reflect the changes suggested.
Normally, I wouldn't declare this a separate draft, especially since I published an earlier draft for this SRFI today, but for some reason I decided to this time, as draft #4. It's probably because I have a soft spot for SICP.
In any case, everyone should feel free to look at the current draft, which incorporates Vladimir's latest pull request.