A little while ago, I was trying to figure out how to programmatically create an Information Management Policy when I came across this document entitled, [MS-WSSCAML]: Collaborative Application Markup Language (CAML) Structure Specification, and let me just say, "WOW".
I checked my most recent SDK installations and it doesn’t look like this document is part of the SDK. Instead, it is available as part of the Open Specifications section of the MSDN Library. Within are a few dozen documents describing the complete set of protocols and schemas used in SharePoint!!!
This is going to keep me busy for awhile.