[johncoltrane]

"ctx" is a very common name for the "context" with which you work when doing stuff in <canvas>. There's nothing magical about it.

Also it's defined at the bottom of the script which, I admit, is a bit weird:

    if hasattr(canvas,'getContext'):
        ctx = canvas.getContext("2d")

from html import * looks bad, I agree, but I believe they did that to allow us to play with their toy from the console.