> I think we should instead introduce a brand new "syntax".  This new
> syntax should indeed include a way to give names to some "rules" (or
> groups of rules) so they can be enabled/disabled by the user.

Okay, but this doesn't seem that hard to retrofit into the current
system.  We could allow a keyword-pair :name SOMETHING in the elements
of `font-lock-keywords' (this metadata can be discarded upon
compilation, so not many changes are needed in font-lock.el).  Then the
user can enable or disable things by name.

> Whoever designs this new set of rules would do well to study other
> editors's approaches to this problem to benefit from some of the
> advantages of the solutions they chose.

This is wise.