Re: [Emacs-diffs] master c4151eb: Improve the optional translation of quotes

[Eli Zaretskii <eliz@gnu.org>]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Thu, 25 Jun 2015 17:59:58 +0300
> 
> On 06/25/2015 05:05 PM, Paul Eggert wrote:
> 
> > Also, it's not clear how the overall approach would work on limited
> > displays that don't have alternate fonts and/or colors.  Suppose, for
> > example, that the user is running 'emacs --color=never' on a character
> > terminal?
> 
> I thought this was implemented somewhere in the display engine? If not, 
> it could be.

I didn't track this discussion, so forgive me if what I say below
makes no sense.

With that caveat, since you (AFAIU) are talking about using the
font-lock mechanism for producing effects other than color, whether
the terminal supports colors should not bother you.  That's because
the actual expression of the faces that have color attributes happens
on the lowest level of terminal-specific parts of the display engine,
and the rest of display doesn't care -- it manipulates faces, not
colors.

> Or someone could tell me how to check whether curly quotes are 
> undisplayable in Lisp, and the rule will perform no substitutions, for 
> instance.

I think you want char-displayable-p.