Anyway, here's an article that supplements the FreeBSD manual entry: The X Window System:
ONLamp.com: Building an X Server and a Window Manager [Jun. 21, 2000]
A little known fact - I was a developer on the original X Window system, way back in the days of MIT's Project Athena, where it all began. Actually, I wasn't an official developer, but I was one of the very first users of X Window System, as I worked as a teacher liason with Project Athena, and one of its centerpieces was X. I wrote a bridge game (unimaginatively called 'xbridge') that for years was on the X distribution tape. That was a looong time ago.....