This module adds XPath-style matching to your object trees. This means
that you can find nodes using an XPath-esque query with match() from
anywhere in the tree. Also, the xpath() method returns a unique path to
a given node which can be used as an identifier.

To use this module you must already have an OO implementation of a
tree. The tree must be a true tree - all nodes have a single parent and
the tree must have a single root node. Also, the order of children
within a node must be stable.

NOTE: This module is not yet a complete XPath implementation. Over time
I expect the subset of XPath supported to grow. See the SYNTAX
documentation for details on the current level of support.