I would like to highlight certain identifiers (such as all uses
of a particular local variable in a function) simultaneously
when the mouse enters any of them.

I've scoured the documentation, and I don't see a way to
accomplish this feat.

Would it be reasonable to add mouse-entered and mouse-left
properties analogous to point-entered and point-left?

Alternately (or in addition), it might be nice to have text
properties analogous to the mouseenter, mouseleave and
possibly mouseover standard browser events, which would
fire at the granularity of pixels rather than characters.

-steve