Documentation?

[Alan Cox]

> > if someone massively resizes a window with backing store (remembering it
> > can be mostly offscreen) your X server explodes.
> 
> Remind us why turning it on for all windows all the time (Composite) is better 
> than for one window? ;o)

There is nothing in composite that requires you redirect everything.

> > Backing store was mostly a mistake at the time of introduction (as
> > opposed to save unders which are a least reasonably resource bounded).
> 
> It was overused, sure, but the idea suggested elsewhere in the thread of using a 
> pixmap and setting that as the window background is essentially doing the same 
> thing (a form of double buffering).

Without all the horrendous complexity and bugs that save unders caused.
The fact you can do it better other ways is even more argument for the
fact they are no longer on. (Not that save unders actually worked
properly in most XFree/Xorg releases in all cases)