sausages.js

// using XPath with namespace
// @see https://developer.mozilla.org/en/Introduction_to_using_XPath_in_JavaScript#Evaluating_against_an_XML_document_within_an_Extension
var ns = "urn:Spam", xml = document.implementation.createDocument(ns, "eggs", null);
xml.documentElement.appendChild(xml.createElementNS(ns, "sausage"));
xml.documentElement.appendChild(xml.createElementNS(ns, "spam"));
xml.documentElement.appendChild(xml.createElementNS(ns, "sausage"));

// there is only one namespace used here.
var resolver = function(namespace) { return ns; };
var result = xml.evaluate("count(//spam:sausage)", xml, resolver, XPathResult.ANY_TYPE, null);

alert(new XMLSerializer().serializeToString(xml) + "\n\n" +
 result.numberValue + " sausages found");


// OSX:
// ----
// Firefox (3.0.3): 2
// Safari (3.1.2): 2
// Opera (9.62): 2