One question I hear a lot is: What XQuery features are supported by DB2 pureXML? My standard answer is "All the features you need!". But what are they?
XQuery itself is built on top of XQuery/XPath Data Model (XDM), the XQuery and XPath Functions and Operators, and some other stuff. The two referenced specs alone are already complex by themselves and guarantee hours of reading fun. A different way of reading through XQuery, its syntax and functions is to go to the DB2 Information Center and its XQuery Reference. It provides a really good introduction into XQuery from the DB2 or database angle. The documentation includes a comparison of SQL and XQuery, an overview of the XQuery data model, and of course the description of expressions, functions, and all the other supported features.
After you are done reading AND trying it out, let me know if you don't agree on "DB2 pureXML: All the XQuery features you need"...