Other Software

PyPointers	Implements part of the XPointer spec, allowing you to point to portions of a document, and if you combine this with a DOM representation of your doc, you might be able to get what you need.
tmproc	tmproc is an implementation of the new international standard ISO/IEC 13250 Topic Maps, containing a set of classes that represents a framework for doing topic map processing in Python.
XML Toolkit	Contains a client/server XML processor, and a WIDL implementation.
XSL-Pattern	An implementation of the pattern subset of the XSL working draft of 16-December-1998.
LT PyXML	A Python module which interfaces to LT XML, a fast validating parser written in C.