> What does it do?

Have a look.

 > If it makes the frame a bit smaller than fullscreen it will not work on X or NS.  There fullscreen is indeed fullscreen and there is no way around it (well easy way).

Fullscreen is fullscreen and maximized is maximized.

 > If it distributes the extra pixels elsewhere than at the bottom, I would assume only the display engine would need to be modified.

Your assumption is wrong.

martin