ExtensionElement is now a marker interface that requires all implementation non-abstract classes to carry a static final QNAME field (of type QName). This is verified by a new unit test. Also FullyQualifiedElement is renamed to simply XmlElement. XmlElement is used over ExtensionElement when implementing classes do not statically know the qualified name of the XML elements they represent. In general, XmlElement should be used sparingly, and every XML element should be modeled by its own Java class (implementing ExtensionElement).