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

[Paul Eggert]

Eli Zaretskii wrote:
> > What do you think of using capital X for hexadecimal escapes with at
> > most two digits? That way, "\X905" would be a two-character string,
> > which is what is wanted here. Or we could use small h for hexadecimal,
> > and "\h905".
> I'm okay, but I'm not sure I understand how does this fix your
> problem.  Can you explain?

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.

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.

This would fix my problem, since I would continue to be able to copy text 
displayed in a terminal window, and paste it into an Emacs string, and get the 
text unaltered even if display-raw-bytes-as-hex is t.