Instances of this class hold double-precision homogeneous 4x4 transform matrices. Such a matrix can move a thing to any point in space, orient it to point any direction, and scale it to any size, among other things. Skandha4 uses instances of this class whenever a position and orientation need to be defined -- in particular, to define the positions of cameras, lights, and things.
MATRIX44s support a number of different messages for specifying the contents of the matrix, ranging from high level commands which say essentially "I want to be looking at the following things" right down to low level commands which stick specified floating point values directly in the array.
One particularly handy class of high-level positioning commands are the :TURTLE-* messages, which implement a form of 3-D 'turtle' graphics, letting you move things relative to their current position and orientation with simple "move forward in the direction you're pointing" type commands. These messages make flythroughs easy to write.