Re: Supporting stylistic sets

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuri Khan <yuri.v.khan@gmail.com>
> Date: Sat, 24 Sep 2022 23:42:33 +0700
> Cc: समीर सिंह Sameer Singh <lumarzeli30@gmail.com>, 
> 	emacs-devel@gnu.org
> 
> On Sat, 24 Sept 2022 at 23:15, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> > I'm sorry, I still don't understand.  (I'm not an expert on fonts, so
> > I'd appreciate a slightly more detailed explanations.)  Are you saying
> > that each tag can be used by a single character in a font?  IOW, no
> > feature tag can ever be shared by two or more characters in a font?
> 
> As I understand it, the font has instructions like “if stylistic set X
> is in effect, use glyphs Y1, Y2, …, Yn for characters Z1, Z2, …, Zn”.
> Depending on the font designer’s whim, there could be separate
> stylistic sets for each character, sets for multiple characters
> similar in shape, and/or sets for a group of characters where the user
> is unlikely to want to control each character separately.

"Unlikely" doesn't fly with Emacs users.  Someone will want to do just
that.  AFAIR, MS Office allows the user to select variants separately
for each character.

And if we want to support only the "likely" use cases, then the idea
of a special text property seems more attractive, since that means
entire segments of text will have the same collection of stylistic
sets.