4. Level Map Models  4.1 Description of .BSP Files  4.1.1
General description of level BSP Maps  The BSP maps are meant to
be generated automatically. They are described here only for the
purpose of helpin you write a BSP generation tool. If you are
only interested in building Quake editors, please read the
description of Level Maps instead.  The level BSP maps are
stored in files with extension .BSP (for Binary Space Partition
Tree). Those files need not necessarily contain level maps, they
can also contain the definition of any entity that is not
supposed to be modified during game play.  Since a BSP based
model requires the calculation of a BSP tree, and this
calculation is tedious, these models are not used to store
definitions of monsters, players, or anything that can change
shape during game play. But you could use them for a model of a
big rock, because that rock isn't gonna be modified...
Moreover, there are no frames associated to a BSP based model,
contrary to what happens for Alias models: it's j