bug#16915: 24.3.50; [ruby-mode] Comments in regexps using the extended syntax are not font-locked properly

[Dmitry Gutov]

On 10.03.2014 16:40, Stefan Monnier wrote:
> We usually use syntax-tables for that.  They do provide more flexibility
> than needed (so far), such as making it possible to allow different
> commenting conventions within the new context.  But it seems like
> a "simple" way to handle the problem, so the extra generality is a bonus.

To handle this part of the problem (literals within literals), yes, 
certainly.

> > (but - and this is a change from certain other multi-mode uses - still
> > fontify uncommented text inside them with the regexp face).  But in the
> > general case, we would at least want to be able to change
> > font-lock-keywords, too.
>
> `font-lock-keywords' can use `syntax-ppss' to decide which rules to use
> (since syntax-ppss would have to include the "context state" somewhere
> in its output).  It's not terribly convenient to do currently, so we may
> want to provide a new replacement for font-lock-keywords which makes it
> easier (and avoids relying on "eval" while we're at it).

If we're speaking of multiple modes in general, syntax-ppss might not be 
enough to determine which keywords to highlight. Even if it includes 
information about new syntax classes.

Suppose we have an HTML file with <script> and <style> tags inside. 
Would points inside of these tags have different states? What might be 
the difference between them?

Would some font-lock code compare syntax table reference attached to a 
syntax class, with a syntax table it wants?