[HarfBuzz] Ligatures

[Eli Zaretskii]

> From: Khaled Hosny <dr.khaled.hosny at gmail.com>
> Date: Sat, 23 May 2020 20:54:15 +0200
> Cc: harfbuzz at lists.freedesktop.org
> 
> > We pass to the shaper the part of text that matches the regexps you
> > can see at the end of misc-lang.el, then display the glyphs the shaper
> > returns.  The above description is a high-level overview; there are
> > many details that I cannot describe in a short message.  For example,
> > for Arabic, when we get back the grapheme clusters, we lay them out,
> > then skip to the end of the text that we passed to the shaper.
> 
> You mean this:
> https://repo.or.cz/emacs.git/blob/HEAD:/lisp/language/misc-lang.el#l78
> 
> I’m not sure how can I read it, but it seems to be missing the entire Arabic Extended-A and Arabic Mathematical Alphabetic Symbols blocks. I’m not also sure how it would handle using combining marks from other blocks with Arabic text (say putting U+20D6 over an Arabic letter).

If you can suggest improvements to those patterns, please do, and
thanks.