David Frey wrote:

The problem I think I am having is that my extension function expects a
string, but I am passing it a node-set. I want to convert the node-set
to a string rather than changing the extension function to accept a
node-set as a parameter. Is this possible?

Well what kind of string do you want, do you want to serialize the nodes back to XML markup? That has been done, for instance http://lenzconsulting.com/xml-to-string/.

String extensionFunction(String inputXml)
{
    MyObject x = new MyObject();
    x.unmarshal(inputXml);
    return x.someComplexOperation();
}