bug#41006: 26.3; regular expressions documentation

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Fri, 8 May 2020 03:10:45 -0700
> Cc: mattiase@acm.org, 41006@debbugs.gnu.org, rtm443x@googlemail.com
> 
> In the user manual, perhaps we could re-organize what we have now
> (excluding other subsections for the sake of brevity):
> 
> * Searching and Replacement
> ** Regexp Search::             Search for match for a regexp.
> ** Regexps::                   Syntax of regular expressions.
> ** Regexp Backslash::          Regular expression constructs starting with ‘\’.
> ** Regexp Example::            A complex regular expression explained.
> 
> Into something like:
> 
> * Searching and Replacement
> ** Regular Expression Search   Search for match for a regexp.
> *** Regexp Syntax::             Syntax of regular expressions.
> *** Regexp Backslash::          Regular expression constructs starting with ‘\’.
> *** Regexp Example::            A complex regular expression explained.

Is "Regular Expression Search" just a parent node of its children, or
does it have content of its own (apart of the menu)?  If the former,
we need a subsection about searching with regexps, after we describe
the regular expressions.  If the latter, then do you suggest to
describe the search before describing the regexps themselves?