Re: Can watermarking Unicode text using invisible differences sneak through Emacs, or can Emacs detect it?

[Eli Zaretskii]

> From: Richard Stallman <rms@gnu.org>
> Cc: psainty@orcon.net.nz, luangruo@yahoo.com, emacs-devel@gnu.org
> Date: Thu, 20 Jan 2022 23:13:30 -0500
> 
>   > Users and readers of certain scripts cannot use such a simplistic
>   > solution, which is basically only suitable for plain ASCII text.
> 
> I am no expert on this issue, but I do edit languages such as French
> and Spanish which use non-ASCII characters.  It seems to work fine.  I
> never insert zero-width characters, at least not knowingly.  Would
> they be inserted without my knowing?
> 
> If not, I think that some non-ASCII text works fine.

You are using a very restricted subset of non-ASCII characters, and
only on text-mode terminals, so you may never meet these characters or
see their GUI effects.  But we are talking about the Emacs defaults,
not about what is good enough for your personal usage limited to your
use patterns and display capabilities.

> Emoji show up on my terminal as diamonds, since it can't display them.
> So do the ligatures.  Ideally we could display the ligatures as two
> letters.

The way to tell the display engine (any display engine, not just that
of Emacs) not to ligate is to have the ZWNJ character between the
characters that we don't want ligated.  That's one of the legitimate
uses of that zero-width character.

>                                                Emacs should be able to do
>   > better.
> 
> It would be very nice to do better,  What would we do?

See textsec.el.

> Perhaps we should convert ligatures on file input-in into digraphs,
> and convert digraphs on file output into ligatures when using some
> coding system.

People nowadays _do_ want to see ligatures, so disabling them by
default would be a step back.