Safari XML issues

The scenario is this:

For Opera and Firefox, I can rely on the XUL library objects for working with the XML DOM.
One of the functions of the DOM I use to select a single node from an XML document using xpath is the evaluate() function.
Safari does not support this function, at least not as described by the XUL documentation.
What I need is a way to select a single node from an XML document using xpath in Safari.

Here's the documentation I used for the Mozilla based browsers, which Opera also seems to borrow from:
www.xulplanet.com/references/objref/XMLDocument.html