Documentation?

[Alan Cox]

> Dropping support for automatic backing store while at the same pushing
> for a design, composite, that is all backing store all the time means
> one of three things : lazyness, incompetence, or a big honking design
> issue in the server.  So, which one is it?

Backing store has long been off by default in Xfree/Xorg. Fundamentally
its a dumb design issue in the concept of backing store - it means the
server has to consume huge amounts of memory keeping copies of stuff and
if someone massively resizes a window with backing store (remembering it
can be mostly offscreen) your X server explodes.

Backing store was mostly a mistake at the time of introduction (as
opposed to save unders which are a least reasonably resource bounded).