Re: jit-lock refontifies too much

[Richard M. Stallman]

     > It would be better just to keep comparing until you reach a line that
     > previously was fontified.  After all, the line that was not fontified
     > before certainly should get fontified, if it is on the screen.  But a
     > subsequent line that was previously fontified may not need to be
     > changed.
     >

    This might work for a single window on one and the same buffer.  With
    two windows there might remain some unfontified stretch between the
    portions shown in the windows.

So what?

     > That is why I suggested recording these ppss values in text
     > properties of the first character on a line--so that they would stay
     > around for comparison later.

    That would be fine.  But recording these properties for each and every
    line fontified would introduce too much overhead.

I suspect think it is comparable to the amount of space used by
font-lock mode now.  Maybe less.  If so, why is it too much?

     > Another possible advantage is: if things are not in sync for the first
     > line after the end of the changed text, it might be in sync on a
     > subsequent line, and that could avoid refontifying most of the lines
     > on the screen.
     >

    I can think of two interpretations for "things are not in sync":

It means "the before and after ppss values do not match".

You're arguing this can't happen very easily.  Maybe that is true.