76.120.36.31: Info on the IGS protocol itself? (2013-09-06 08:13) [#9843]

I'm writing a new PandaNet client for Windows 8 and Windows Phone 8 called The Game of Go (available for Win8 now-shameless plug), but I can't seem to find documentation on the IGS protocol itself. I see the docs on the end user commands, but not much more. Here is an example of the data from the server:

9 Set client to be True. 1 5 9 Set review to be True. 1 5 9 Set newrating to be True. 1 5

21 {friend1234 5k+? has connected.} 1 5

I'm curious as to the sequence to log in, how errors are conveyed, what all the codes mean, that sort of thing. It seems pretty simplistic, but it's gonna be a lot of reverse engineering without documentation.

Any help is appreciated!