Private Use areas

[Eli Zaretskii via Unicode]

> From: jsbien at mimuw.edu.pl (Janusz S. Bień)
> Cc: unicode at unicode.org,  richard.wordingham at ntlworld.com
> Date: Thu, 23 Aug 2018 21:47:03 +0200
> 
> I'm very glad you join the discussion.

I'm sorry for not joining sooner.  In my defense, I missed the
reference to Emacs, and the rest of the discussion is not really
interesting for me, as using PUA for new characters is not something I
have interest in or experience with.

> My needs are very simple, for example C-x 8 Return LATIN CAPITAL LETTER
> A WITH MACRON AND BREVE [MUFI] should yield the character with the code
> E010. I can provide the list of names and codes.

So you'd like to extend "C-x 8 RET" to recognize names of additional
characters and associate them with codepoints in the PUA area?  That
shouldn't be hard to add.  But is that all? won't you also want to
tell Emacs about the properties of those characters? or be able to set
up fonts for displaying them?  IOW, would it be okay to have these
characters be "second-class citizens" in Emacs?

> > It is true that the Unicode related data is produced at build time,
> > but only some of that is actually recorded in the Emacs binary, the
> > rest is loaded upon demand.  But all the data is stored in data
> > structures that are mutable, given some Lisp programming.
> 
> I never was fluent in Lisp programming and by now I forgot almost
> everything I knew, so it's not a task for me. I was thinking about
> submitting a feature request, but I forgot also the proper procedures to
> do it.

The proper procedure is to type "M-x report-emacs-bug RET" and then
describe the feature(s) you'd like to see added/improved.

> Moreover I had the impression that I'm the only person who needs
> it...

That shouldn't stop you.  Many a feature in Emacs started as a request
from a single individual.

> > (It is not clear to me which part of the Unicode data you would like
> > to change; are you talking about adding characters to the list of
> > those defined by Unicode?  If you are using the PUA codepoints, it's
> > possible that you will need to update Emacs's notion of PUA as well.)
> 
> Yes, I would like the PUA codepoints to be handled analogically as the
> proper ones. What do you mean by Emacs's notion of PUA?

Emacs knows about the PUA regions of the Unicode code-space, and
treats those codepoints specially.  The features you request will
probably need to affect the PUA region as well, because the codepoints
you use should no longer be treated as PUA.