Re: Display of undisplayable characters: \U01F3A8 instead of diamond

[Eli Zaretskii <eliz@gnu.org>]

> From: Emanuel Berg <incal@dataswamp.org>
> Date: Sat, 27 Aug 2022 00:56:31 +0200
> 
> And in particular because we had the old style already so we
> should know how to do that already

No, we didn't "have the old style".  We had a bug: we sent to a
terminal a character code that it cannot display.  That should never
happen in Emacs.  That bug is now fixed, and such characters are
considered as not displayable by the terminal, as they should be.

We are not going back to the situation where we sent to the Linux
console character codes for which it couldn't produce valid glyphs.
People who suggest sending U+FFFD to the Linux console should first
verify whether the console is capable of displaying that character.
One way of verifying this is to type

   C-x 8 RET fffd RET

in an Emacs session which displays on the Linux console, and see if
that shows the diamond-like glyph or the \Unnnn thing.  If it's the
latter, it means the console doesn't support that character, and we
cannot send its code from Emacs.  We should instead send something
else (provided that someone submits patches to send that "something").