Re: linum.el?

[Richard Stallman]

    I still firmly believe that these cases should be handled via jit-lock
    and/or fontification-functions and/or some extension of them.

If that works, I have nothing against it.  But I think it will be
difficult to go that way.  fontification works with text properties,
and linum.el uses overlays.

I don't think we want to use text properties for linum.el.  When you
copy fontified text into a buffer that allows arbitrary faces, it
stays fontified, and that is the right thing.  But we don't want it to
bring along line numbers from another buffer.