XPath
From Friend2Friend Wiki
XPath is a W3C standard for specifying expressions about XML documents, and has been a recommendation for the last 10 years. If you are new to XML technologies and looking for a place to start learning, you could do a lot worse than start with XPath, since not only is it simple and effective, it is a core component of both XSLT and F2F. Almost all the processing directives are XPath expressions, sometimes returning nodesets, sometimes strings, sometimes either is allowed.
