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

[martin rudalics]

>     (2) Modify `jit-lock-after-change' appropriately by, for example, 
inserting
>
>        (forward-line (- font-lock-lines-before))
>
>     before
>
>        (setq start (line-beginning-position))
>
> That seems like the right fix.  Why do you think it isn't?
>
>

Because this means that every time I insert one character, redisplay
would refontify `font-lock-lines-before' in addition to the current
line.  I suppose that the impact of this variable has not been noticed
so far because jit-lock doesn't consider it.

On the other hand, jit-lock wouldn't be able to handle this variable in
the same way as font-lock does: font-lock refontifies immediately in the
after-change hook.  jit-lock's after-change hook would only reset the
fontified property to nil.  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".