bug#41006: 26.3; regular expressions documentation

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Tue, 5 May 2020 19:12:50 +0200
> Cc: jan <rtm443x@googlemail.com>, Stefan Kangas <stefan@marxist.se>,
>  41006@debbugs.gnu.org
> 
> Aim for all in a single node, using subheadings as appropriate

I usually prefer not to use subheadings, because Info doesn't have
commands to go to a subheading.  Can we make each subheading a
subsubsection and give it a node?