bug#6227: Color isearch regexp submatches differently

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: juri@jurta.org,  lennart.borgman@gmail.com,  6227@debbugs.gnu.org
> Date: Sun, 20 Sep 2020 21:45:38 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Lars Ingebrigtsen <larsi@gnus.org>
> >> Cc: juri@jurta.org,  lennart.borgman@gmail.com,  6227@debbugs.gnu.org
> >> Date: Sun, 20 Sep 2020 15:47:13 +0200
> >> 
> >> Now pushed.  The faces should be legible both on dark and light
> >> backgrounds, but they aren't very...  pretty.  Feel free to tweak them.  
> >> :-)
> >
> > What bothers me is that faces isearch-group-6 to isearch-group-9 are
> > not defined.  Should we define them?
> 
> I'd rather go the other way, to be honest -- just leave group-1 to -3,
> perhaps.  I think it's rather unusual to have a that many sub-groups
> interactively...

That's true, but the problem which bothers me is that customizing
search-highlight-submatches alone to a larger value is not enough.  I
don't think any other customization we have requires users to create
faces or similar objects.