Th X3D source does contains the documentation as well.
It says:
/*-- Author : Mark Spychalla*/
/*
Copyright 1992 Mark Spychalla
He says (see that source again):
" ...
Don't think I usually code in the gerberized fashion that X3D demonstrates.
X3D was written for speed at any cost. My goal was to write the fastest 3D
object viewer that I could, period. Regular programs ought to be written
with different goals in mind such as:
1) A program has excellent documentation that ANYONE can read.
2) A program when released has no strange "features" or bugs.
3) A program is robust and handles ALL extreme and unusual cases.
4) A program is written in phases and modules with hard tests for each one.
5) A program is written for any user who doesn't need special knowledge
to use the program.
6) A program has well defined user requirements and functional specifications.
7) A program is written with regard to future expansion and integreation
with other systems (portability).
.. "
Apart this one can press "m" to pop the "Help X3D menu" up.
Hope this helps,
Valery