Regardless of how long I've been working with SharePoint, I have always had to go back to the CAML reference in the WSS v3.0 SDK for the CAML reference for syntax and such. This could be found in the GENERAL REFERENCE \ REFERENCE \ CAML CORE SCHEMAS section of the SDK.
As you might have noticed, the SharePoint 2010 SDKs have been completely reorganized... which is a great thing (no secret I'm a big fan of the new docs). However with the change it can be a bit tricky in trying to find what you're looking for in the new SDK. Best way to do it I've found is to find the equivalent thing in the MSDN online library using search. Then you'll see a link at the top pointing to the same page in the 2010 documentation.
For the CAML reference, that's been moved into the GENERAL REFERENCE \ SERVICES REFERENCES \ CAML CORE SCHEMAS section.