XPath 3 and XQuery 3 are powerful and great technologies to query XML if you need that stuff. The problem is that most implementations cover XPath 1.0 because I guess it is too difficult (i.e. time consuming and involved) to produce a 2.x or 3.x implementation, let alone with full W3C XML Schema support. There is also BaseX which implements XQuery 3.x which is a nice native XML database. I really dig XML and its technologies. I wish XQuery 3.x was available everywhere.