bug#50766: Regexp paren pairs in query-replace-regexp prompt should be highlighted

[martin rudalics]

> I think that it would help users a lot when constructing regexps, so it
> would be very welcome.

OK.  I'll try to cook up something useful.

>> It would not handle 'blink-matching-open'.
>
> Is there any way to make that work, too?

Hardly.  'blink-matching-paren' is not timer-based.  Doing any parsing
in between would slow down typing.

> Some people don't like
> show-paren-mode, but use 'blink-matching-open' instead.

With 'blink-matching-paren' on do C-M-% and type [)].  People who use
'blink-matching-paren' do not type complex regexps.

martin