bug#41006: 26.3; regular expressions documentation

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Stallman <rms@gnu.org>
> Date: Thu, 07 May 2020 22:49:22 -0400
> Cc: mattiase@acm.org, 41006@debbugs.gnu.org, rtm443x@googlemail.com
> 
>   > My proposal is to include "how to use them" inside the chapter called
>   > "Regular Expressions".  Is there any reason not to do that?
> 
> Now we have
> 
> >   > * Regular Expressions::   Describing classes of strings.
> >   > * Regexp Search::         Searching for a match for a regexp.
> 
> We could convert Regexp Search into a subsection under Regular
> Expressions.  I don't see any harm in doing that.

Let's first decide whether we are talking about the Emacs user manual,
the ELisp reference manual, or both.  The current organization of this
stuff is slightly different in each one.  The OP meant the user
manual, AFAIU.

To answer the specific question you asked: this is all part of a
chapter called "Searching and Replacement" in the user manual and
"Searching and Matching" in the ELisp manual.  So having there a
section called "Regular Expressions" which would include a subsection
about regexp search makes less sense to me than the other way around:
have a section "Regular Expression Search" which would start with
syntax of regexps and go on to a subsection that describes the regexp
search facilities (it should then probably include the "POSIX Regexps"
section as well).