bug#19368: 25.0.50; NSM prompt is not self-explanatory enough

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 19368@debbugs.gnu.org
> Date: Fri, 05 Feb 2016 18:46:13 +1100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I don't think you should be bothered by that, because 'underline' is a
> > standard face, and every terminal expresses it as best as they can.
> > Just use it.
> 
> But underline in addition to [t]his?
> 
> I guess I'm asking whether there are terminals that don't do underline
> at all, and I would guess that there are...  so we need to do [t]his on
> all terminals, unless we have a way to query the terminal for whether it
> supports underline?

I think you want this:

  (display-supports-face-attributes-p '(:underline t) FRAME)

This returns non-nil only if underline is supported "in some way" by
FRAME's display.  Where "in some way" means that the appearance will
be different from the default face.