bug#51016: 28.0.50; 'diff-font-lock-prettify' breaks display of outline headers

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Eli Zaretskii <eliz@gnu.org>,  51016@debbugs.gnu.org,
>   orontee@gmail.com,  juri@linkov.net
> Date: Sun, 19 Dec 2021 12:00:14 +0100
> 
> Kévin Le Gouguec <kevin.legouguec@gmail.com> writes:
> 
> > Right; unfortunately, in addition to this *conceptual* understanding of
> > form feeds, *functionally* they are treated as level-1 headings, with
> > the unfortunate consequences we highlighted.
> >
> > As you point out, they are page delimiters; if we were to take them out
> > of outline-regexp, page commands (navigation, marking, narrowing) would
> > keep working just fine!
> 
> Yes, I don't really see any reason to keep ^L in the outline regexp,

I do, so please don't make that change unconditionally.