Re: jit-lock doesn't honor font-lock-lines-before

[Richard M. Stallman]

    Because this means that every time I insert one character, redisplay
    would refontify `font-lock-lines-before' in addition to the current
    line.

Would that be bad?

      Whether and when these lines are refontified
    would be _also_ decided by the redisplay engine.  And the latter doesn't
    know about `font-lock-lines-before'.  For example, editing the first
    line in a window would not "include the line before in refontification".

This is a good point.  However, it can probably be fixed by a change in
the fontification function--when it is called, it should extend the starting
point for refontification upward by the specified number of lines.
(This might be the only fix needed.)