bug#27270: display-raw-bytes-as-hex generates ambiguous output for Emacs strings

[Eli Zaretskii]

> Cc: npostavs@users.sourceforge.net, 27270@debbugs.gnu.org,
>  v.schneidermann@gmail.com
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Fri, 9 Jun 2017 16:44:46 -0700
> 
> The idea is to add a new \X escape for character constants and strings. This 
> escape would allow at most two hexadecimal digits, rather than the unlimited 
> number of digits that \x does. For example, the Lisp string "\XABC" would be 
> equivalent to the Lisp string "\xAB\ C", that is, it would be a two-character 
> string containing the character U+00AB LEFT POINTING GUILLEMET followed by 
> the 
> character U+0043 LATIN CAPITAL LETTER C.

So your proposal would mean a change to the Lisp reader to support
such escapes, right?  If so, isn't such a change
backward-incompatible?

> Also, display-raw-bytes-as-hex would cause raw bytes to be displayed with 
> this 
> new X escape, rather than with with the x escape.

It could only do that for codepoints below 256 decimal, so that
limitation should be taken into account when deciding on the proposal.