Standard Definitions - Where Can I Find Info?

Imported from previous forum

Hello, all.
I’ve been asked my my employer to evaluate the FIX protocol, particularly the XML implementation. I have acquired the FIX 4.1 Specification and the XML DTDs, but I’m wondering if there is additional definitional material?
For example, is there any kind of process definition to define valid exchanges of messages? Are there additional definitions of the fields? Some of the defintions I have found so far are somewhat confusing and/or vague to me.
Thanks for any help!
P.