Changes

It would probably be a good idea to include a addNamespace(namespaceURI, prefix) method to the IDL, to point into the resolver's namespace map. -- Alex Vincent

Mozilla's XPath implementation doesn't currently support crossing boundaries between framed content and the container frame element, or between real content and its anonymous children. Our XPath and XPathGenerator can be reasonably expected to support this in the future, so now's the best time to come up with a function syntax for doing this.