> face on matched regions of the buffer. It should just add overlays. The
> code should get simpler, including removing the overlays when you
> un-highlight matches, because that's just `(mapcat #'delete-overlay
> existing-overlays)`.

Better would be to add "text-property planes".  So font-lock could
add&remove its `face' property and highlight-symbol could add&remove its
own `face' property without conflict.

I think this would make a nice GSoC project.


        Stefan