Documentation on XFree86-modules

[Are-Harald Brenne]

First: Where can I find documentation on the different modules that are specified under the modules-section of XF86Config? I want to know what they do and what options each of them may 
I've looked through all the man-pages, but I couldn't find anything about it.

Second question; are graphic card drivers, specified in the device section of XF86Config, operating system specific? An XF86Config-file i got from my Mandrake-days contains a lot more options in the device-section than the man-page on freebsd shows.

Cheers,
Are-Harald