And this is why I read (free|open)bsd's cvsweb repo when I'm curious as to how things are implemented. I used to visit that repo in university when I was bored just to read some clear, concise, well-documented code.

I used to use and love FreeBSD (Since switched to OS X as desktop os, still run FreeBSD servers), but OpenBSD source code just looked more approachable.

McKusicks' wonderful book and video course helped.