RE: overlays vs text properties

["Drew Adams" <drew.adams@oracle.com>]

I don't have much to offer here that hasn't been said already.

FWIW - It sounds to me like overlays are best suited for what you want to do.

Checking for point movements in/out of the overlay: How often and when do you
need to do it?

If you need to do it after each user interaction, then maybe do it in
`post-command-hook'.  If you can avoid using that hook, great (it tends to be
overused, in general).  But if that's when you need to check, then that's
probably the best approach I can think of.

(To check, just see whether point is inside the overlay.  To know whether that
state represents a change you will likely need to save the last in/out state and
compare.)