AFAIK fvwm-crystal is just a regular fvwm, but entirely configured and complemented with some applications. Those are totally independent from fvwm itself.
Therefore i assume any config option used in fvwm should also apply in fvwm-crystal's config.
The manpages of fvwm are exceptionally thorough and well documented and there's always the fvwm forum (
http://fvwm.lair.be/) where several fvwm-crystal questions are asked (and answered ..
) And check the FAQ on
http://www.fvwm.org.
As fvwm is a very powerful but not that easy to configure windowmanage, check out other configs as an example and skim the manpages.
