RE: how to test whether region is active during a mouse event?

[Drew Adams]

P.S. I suppose I could assume the down, down, click scenario and record the
region info for only the first down. IOW, I could save some state. But I'm
hoping for something a bit cleaner and simpler.

Also, I had the impression (not sure, but I think I saw this when testing) that
if the button-click is in a different frame from the one that had the focus,
then a `switch-frame' event replaces the first `down'. If that kind of thing
happens, then I can't assume a down, down, click event sequence.