bug#49844: Highlight non-selected minibuffer prompt

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Date: Thu, 05 Aug 2021 00:32:19 +0300
> Cc: 49844@debbugs.gnu.org
> 
> > Can't we just put it in minibuffer.el?  (But then there should probably
> > be a user option to switch it on/off.)
> 
> Ironically, minibuffer.el is intended for code that deals with
> completions.  Its first line is
> 
>   ;;; minibuffer.el --- Minibuffer completion functions

That's not carved in stone, though.  We could change that heading
accordingly, and start adding stuff to minibuffer.el that doesn't
necessarily deal with completion.

> But most code that deals with the minibuffer
> is somewhere in the middle of simple.el.

Which is somewhat sub-optimal, I think.

> Maybe it would make sense to create a new file with the name e.g.
> minibuf-x.el as a mixed bag of tiny minibuffer features?

I don't think a new file is justified at this time.