Toning down font-lock

[Augusto Stoffel]

I would like to suggest extending `font-lock-maximum-decoration' so that
setting it to a negative number discards all major-mode keyword
fontification, keeping only syntactic highlight (i.e., strings and
comments).

I've been using such a setting for a long time and it's quite pleasant.

I'm also wondering if there is a more fine-grained mechanism to pick and
choose font-lock rules.  I guess not, so should there be one?

In my setup, I do lose some things that I find useful, such as highlight
of regexp grouping constructs or symbol names inside docstrings.
`font-lock-maximum-decoration' doesn't allow to activate these things
without activating coloring of functions and keywords, which I don't
like.  Making some font-lock faces equal to the default face is also a
very coarse measure, and leads to other problems, since the font-lock
faces are often abused for other purposes.