bug#64759: Broken faces

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: maurooaranda@gmail.com,  64759@debbugs.gnu.org
> Date: Mon, 24 Jul 2023 20:35:17 +0300
> 
> >> No, it's not the same.  The latter uses a white background on the mode 
> >> line.
> >
> > So I ask again: what is the semantics of nil in this case?  We cannot
> > have in Emacs something that triggers undefined behavior, let alone
> > use it in our own sources.  The semantics of this must be known and
> > documented before we can use it.
> 
> The semantics of nil could be the same as '((t nil)).

And what is the semantics of '((t nil)) ?  What attributes will the
face have when realized?

> Do you agree that currently the value '((t nil))
> should be used for faces without default face attributes?

Yes, I think so.  If no better face to inherit from is available in
each such case, that is.