bug#55319: 28.1.50; Abugida not rendered correctly (MacOS)

[Eli Zaretskii <eliz@gnu.org>]

severity 55319 wishlist
thanks

> From: Kai Ma <justksqsf@gmail.com>
> Date: Sun, 8 May 2022 19:45:04 +0800
> 
> I installed the Crisa Regular font [1] (font name is “Crisa”) and tried to type some zbalermorna [2] (an abugida) into Emacs.
> 
> However, the positions of the vowels are not correct, as shown in the attached screenshot obtained in emacs -Q.
> The vowels should be right above the constants.
> 
> The correct rendering can be seen at this web page [3] (using a decent modern Web browser).
> I can confirm other applications using the system GUI toolkit works, e.g. TextEdit.app.

Emacs doesn't OOTB support scripts whose characters are not in
Unicode.  When characters are not in Unicode, their properties and
attributes aren't known, unless someone tells Emacs what they are.

The sites to which you point indicate that this script was created for
an artificial language and its characters use the Private Use Area
codepoints of the Unicode code-space.  So making Emacs support this
invented script will need some work from someone who knows the details
and can submit patches which add these characters and their properties
to the databases Emacs needs in order to handle those characters.