Version 1.1 maintains backwards compatibility with XOM 1.0 while adding a number of important new features including XPath queries, document subset canonicalization, exclusive XML canonicalization, external XSLT parameters, and xml:id support. It also fixes a number of bugs that were present in XOM 1.0, uses less memory, and is two to four times faster for many common operations.
In case you don’t know XOM, it’s an XML API alternative to JDOM or dom4j and very much worth a closer look.