bug#43702: Emacs master: Incorrect highlighting in regexp isearch.

[Drew Adams]

> >> Maybe better to do what Drew proposed: to distinguish the odd groups
> >> from the even groups, i.e. to have only 2 additional faces
> >> (a brighter face like the current isearch-group-1 for the odd groups,
> >> and a darker face for the even groups).
> >
> > To be clear, I didn't propose that.  My code has 8 levels
> > (groups), with 8 faces.
> 
> My intention was to give credit where credit is due.
> Thank you for the idea.
> 
> > What I mentioned about even and odd is for lazy-highlighting.
> 
> Both ordinary and lazy-highlighting matches could be based on
> the same idea of odd/even faces.

They could.  But they shouldn't.

For the current search hit, it makes sense to provide
as much info as possible visually.  That is, in this
context (regexp matching), highlight each of the groups
in a unique way, so they can be easily identified in
the search hit.

The idea behind even/odd lazy-highlighting is to just
provide a rough idea of some of the matching.  The
current search hit should show accurate, complete info
about the match.