bug#63731: [PATCH] Support Emoji Variation Sequence 16 (FE0F) where appropriate

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: 63731@debbugs.gnu.org,  steven@stebalien.com
> Date: Tue, 06 Jun 2023 09:28:04 +0200
> 
> >>>>> On Mon, 05 Jun 2023 19:39:37 +0300, Eli Zaretskii <eliz@gnu.org> said:
> 
>     >> From: Robert Pluim <rpluim@gmail.com>
>     >> Cc: 63731@debbugs.gnu.org,  steven@stebalien.com
>     >> Date: Mon, 05 Jun 2023 17:57:04 +0200
>     >> 
>     >> >>>>> On Mon, 05 Jun 2023 18:35:37 +0300, Eli Zaretskii <eliz@gnu.org> 
> said:
>     >> 
>     Eli> Which forward rules would conflict with a backward rule triggered by
>     Eli> U+FE0E?
>     >> 
>     >> All the ones for the non-emoji codepoints that still need to be
>     >> composed as emoji sometimes, eg U+261D:
>     >> 
>     >> "\N{U+261D}"
>     >> "\N{U+261D}\N{U+1F3FB}"
>     >> "\N{U+261D}\N{U+1F3FC}"
>     >> "\N{U+261D}\N{U+1F3FD}"
>     >> "\N{U+261D}\N{U+1F3FE}"
>     >> "\N{U+261D}\N{U+1F3FF}"
> 
>     Eli> Couldn't we put these in the slots of #x1F3FB..#x1F3FF instead, as
>     Eli> backward rules?  As long as we don't have a forward rule starting 
> with
>     Eli> #x261D, we could have backward rules for it triggered by #x1F3Fx and
>     Eli> #xFE0x, right?
> 
> Yes, we could invert the whole composition rules setup, and make them
> all work backwards, but then it will almost certainly all break again
> with the next release of Unicode. Adding a special case for FE0E in
> font_range is going to be more robust.

I don't think it could break, since such sequences are all likely to
be triggered by special codepoints that follow the U+2xxx characters.
Our win would be a much simpler setup.

But okay, let's try to do it this way.