Re: tabulated-list-init-header and glyphless-char-display

[Eli Zaretskii <eliz@gnu.org>]

> From: Chong Yidong <cyd@stupidchicken.com>
> Date: Mon, 11 Apr 2011 18:31:51 -0400
> Cc: monnier@iro.umontreal.ca, emacs-devel@gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > So we are going to invent a new display feature, just to display 2
> > fancy characters in a specialized mode buffer, and in a way that will
> > support simultaneous display in several different display types?
> 
> Yep.
> 
> > I'd say it's an overkill.  Perhaps we should simply compromise and use
> > ASCII art, or no indication at all.
> 
> I suspect there will be other situations where it's convenient to use
> unicode glyphs in Emacs buffers.  If we can design a sufficiently
> flexible system, I think this is a good investment.
> 
> For example, one could imagine a version of table.el that displays
> 
> ┌─┬─┐
> │a│b│
> ├─┼─┤
> │ │ │
> └─┴─┘
> 
> on graphical terminals, using the Unicode box-drawing glyphs, and
> displays the equivalent ASCII borders on terminals that don't handle
> Unicode.

Then let's extend glyphless-char-display to provide this information.
That is, for each character, it should provide display information
both for GUI and for text-mode displays.  It can do that by providing
an option to have an element of the char-table be a vector of 2
elements, instead of just one value today.  Most table entries will
still be symbols like today, but we could have some of them be
vectors, as in this case and in the case of line-drawing characters.

I think this is better than the text property suggestion, because
glyphless-char-display can be set once and by default, whereas with
text properties each Lisp application that needs it will have to do
that manually.

WDYT?