This is an XML parser based on PHPs built-in xml extension. It supports two
basic modes of operation: "func" and "event". In "func" mode, it will look for
a function named after each element (xmltag_ELEMENT for start tags and
xmltag_ELEMENT_ for end tags), and in "event" mode it uses a set of generic
callbacks.

Since version 1.2.0 there's a new XML_Parser_Simple class that makes parsing of
most XML documents easier, by automatically providing a stack for the elements.
Furthermore its now possible to split the parser from the handler object, so
you do not have to extend XML_Parser anymore in order to parse a document with
it.