Re: Upcoming loss of usability of Emacs source files and Emacs.

[Paul Eggert <eggert@cs.ucla.edu>]

Dmitry Gutov wrote:
> However, if we change \= to \ as the quoting method in substitute-command-keys
> as well, that will be less of a problem. Backward compatibility might be, but
> I've seen no evidence thus far, of \= being used anywhere outside of Emacs core.

The problem with using \\ to quote in docstring sources is not that \\= is 
rarely used; it's that \\X is reasonably commonly used for lots of different 
values of X, and it's expected that \\X normally displays as \X.  If we decide 
to change the meaning of \\` and \\' (but not of \\ followed by other chars), 
then we'll have to change maybe 20 docstrings in the Emacs source code, and a 
few similar changes will no doubt be needed in 3rd-party packages.  This is why 
the current master uses \\= to quote quotes (as \\= has always worked so this is 
compatible with older Emacs).  And it's partly why I originally objected to \\` 
and \\'.

That being said, Stefan is right that \\` and \\' are shorter than \\=` and \\=' 
and in that sense are nicer.

A couple more downsides of \\` should be mentioned, though, before making this 
not-quite-compatible change.


First, \` and \' already have a special meaning in docstring sources (unrelated 
to this issue) and it will be confusing for people to read docstring source code 
like this:

"LISTIFIED is a list representing each topic header and body:

  \`(depth prefix text)'

or \`(depth prefix text bullet-plus)'"

if people know that backslash before grave accent means a grave accent, as in 
the above examples \` would still mean left quote, not grave accent.


Second and more important, here's an example of a docstring that would need to 
be changed:

"Face for characters displayed as sequences using `^' or `\\'."

Presumably this would be changed to:

"Face for characters displayed as sequences using `^' or `\\\\'."

But this would mean that we need to change the meaning of \\\\ in docstring 
sources too, and that's a bigger deal and would affect more than 20 or so 
docstrings.  For example, we'd need to change this docstring source:

"REGEXP must contain at least one parenthesized subexpression, typically
whitespace of the form \"\\\\(\\\\s-*\\\\)\"."

to this:

"REGEXP must contain at least one parenthesized subexpression, typically
whitespace of the form \"\\\\\\\\(\\\\\\\\s-*\\\\\\\\)\"."

I'm not sure this is a good idea.