bug#24594: 24.5; `variable-pitch-mode': accept FACE arg instead of hardcoding the face

[Drew Adams <drew.adams@oracle.com>]

> > > The variable-pitch face is a very general face: it stands for a face
> > > using any variable-pitch font, of which there are gazillions.
> >
> > A single face.
> 
> Yes, a mode that was made for using a single face.  There's nothing
> wrong about that.

Your statement was not about the mode, and neither was my reply to it.
It was about your claim that the face "stands for a face using any
variable-pitch font...".

How a face stands for a face, I don't know.  But there is nothing
more general about this face than any other face.  It, like others,
is entirely customizable.

Nor is it more restrictive than other faces.  As I mentioned, you
can easily customize it to NOT be variable-pitch.

> > The face is hard-coded in the command.  You cannot use the command
> > with a different face.  Being able to customize a face is something
> > else altogether.
> 
> Yes, I understood that the first time.  Reiterating this doesn't help
> in any way.

You mentioned the ability to customize the face as somehow obviating
the command being restrictive (hardcoded to one particular face).
I replied that customizing the face is something else altogether -
irrelevant here.

> > And no, there is nothing special about face `variable-pitch'.  In
> > particular, there is nothing that prevents you from customizing it
> > to a fixed-pitch face.
> 
> Of course.  But why would one want to do that?  It's like customizing
> a color named "black" to have the same appearance as "white".

Who said that one should want to do that?

Naming a face after any of its default attributes (e.g. `red-foreground')
is misguided.

But that's not the point here.  This was in reply to your statement that
face `variable-pitch' "stands for a face using any variable-pitch font."

It doesn't stand for any particular set of faces, at least not according
to the code.  It is just a face like another - entirely customizable.

It might be interesting to have a face whose customization is limited
to variable-pitch fonts.  But (so far anyway) `variable-pitch' is not
that face.

> Anyway, looks like one more of those arguments that go nowhere, so I'm
> out.

Likewise.  You brought in extraneous stuff, to which I replied,
hoping it might help.  I should know better by now, I guess.