Apache processes requests in phases. A handler is a function that processes a particular phase of a request. Handlers are provided by Apache and by its modules, like mod_python.
XML is a fairly simple format. It uses plain Unicode text rather than binary encoding, and all the structures are declared with predictable-looking tags. Nonetheless, there are still enough rules in the XML grammar that a carefully debugged parser is needed to process XML documents -- and every parser imposes its own particular programming style. An alternative is to make XML even simpler. The open-source PYX format is a purely line-oriented format for representing XML documents that allows for much easier processing of XML document contents with common text tools like grep, sed, awk, wc, and the usual UNIX collection.
As part of the ongoing quest to create a more seamless integration between XML and Python, this article presents the xml_pickle module. The author discusses the design goals and decisions that went into xml_pickle and provides a list of likely uses.