Re: font-lock-keywords: matcher function not working

[Raffaele Ricciardi <rfflrccrd@gmail.com>]

On 28/06/13 21:30, Stefan Monnier wrote:
> That's not a search.  It just says "doesn't match here" without saying
> anything about the rest of the text until ^end, whereas a nil return
> value is supposed to mean "nothing found between here and ^end" (just
> as a nil return value of `re-search-forward').

Thank you again, Stefan.  However, I still don't understand. The check
is there because Emacs' regular expressions lack a "look behind"
construct, and the matcher has to check for leading whitespace.  How
is it supposed to look?  I chose to look for leading whitespace
separately, and to choose afterwards whether to return NIL immediately
or to return the result of `re-search-forward' - which at that point
is guaranteed to succeed - but such call is a shortcut to ensure that
the matcher returns information consistent to the requirements of the
font locking engine.  Am I missing something?