Re: mouse-face and help echo support for xterm mouse

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 05 Nov 2020 22:46:32 -0800
> From: Jared Finder <jared@finder.org>
> Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
> 
> >>  (defface mode-line-highlight
> >> -  '((((class color) (min-colors 88))
> >> +  '((((type graphic) (class color) (min-colors 88))
> >>       :box (:line-width 2 :color "grey40" :style released-button))
> > 
> > I don't think I understand the rationale.  With TTYs supporting many
> > colors nowadays, and mode-line-highlight available on TTYs, what is
> > the problem you tried to fix here?
> 
> Are there any TTYs that support :box?  None of the platforms I tested 
> locally on do, they instead just ignore the :box aspect of any face.

That's true, but having conditions where they aren't necessary is not
good for maintenance, because they aren't future-proof: they will need
changes should someone implement the :box attribute for TTYs.  We've
bumped into such problems many times during the last two decades: as
more and more display features (colors, menus, mouse) became supported
on TTYs, we time after time found them not working in some package,
because someone arbitrarily disabled that for TTYs on the assumption
that "TTYs cannot possibly do that".  So attributes that are silently
and harmlessly ignored should not in general be disabled.

If you want, we can add a more reasonable condition, using the
'supports' keyword, requesting specifically support for the :box
attribute.

Thanks.