bug#12054: 24.1; regression? font-lock no-break-space with nil nobreak-char-display

[Drew Adams]

> > That is, the literal string in my code is read as a string 
> > that contains only a single raw byte of octal 240 in place
> > of the 4 chars \240 (and instead of as a string with the
> > multibyte char no-break space).  Is that right?
> 
> Yes.
> 
> > And putting that together with Eli's statement about 
> > insertion ("'insert' treats strings such as "\nnn" as
> > unibyte strings"), I understand that the buffer text
> > after I type `C-q 240' contains a unibyte raw byte, and
> > not the multibyte char no-break space.
> 
> No.  It contains the NBSP.  Try it.

Well, I was saying since the beginning tha that appeared to be the case.  But
you replied that insertion inserted a raw \240 byte.  That red herring threw me
off.

> C-q inserts a multibyte character, unlike '(insert "\240")', for example.

Thanks, I finally got that from what Stefan said.  It would have been clearer if
you had said that from the beginning, since I mentioned `C-q' and you replied
instead about "insert".  Anyway, I understand now.

> Try '(insert "\240")' and then "C-x =" will show a unibyte byte.

Yes, I got it (from Stefan's reply).  But no one mentioned using `insert' or
insertion, except you.  I know you were trying to help, but that just confused
things, for me.

> > I can see how that can be useful.  But I can also see how 
> > it would be useful to have some way of using octal syntax to
> > match multibyte chars.  Isn't there some reasonable way to
> > allow for both?
> 
> Maybe, but we didn't find one, at least not one that would be
> backward-compatible.

OK, that was my question.  Thx.

> > (decode-coding-string "\302\240" 'utf-8)
> > 
> > That allows use of only octal syntax - good.  But it still 
> > doesn't solve the problem for older Emacs versions - they
> > raise the error (coding-system-error utf-8).
> 
> You don't want this, because even if you succeed in producing a NBSP
> in Emacs 22 and older, the result will not match NBSP in other
> charsets.  It's simply impossible with those versions of Emacs.

Got it.  That is the bottom line - the answer to my question.

Thx to all who took the time to help me understand better.