Create a new element (namespaceURI,name), append it
           to current node, then set it to be the current node.
        Keyword arguments:
            namespaceURI -- namespace of element to create
            localName -- local name of new element
            prefix -- if namespaceURI is not defined, declare prefix.  defaults
                to 'ns1' if left unspecified.

def createAppendSetElement(self, namespaceURI, localName, prefix=None):
        '''Create a new element (namespaceURI,name), append it
           to current node, then set it to be the current node.
        Keyword arguments:
            namespaceURI -- namespace of element to create
            localName -- local name of new element
            prefix -- if namespaceURI is not defined, declare prefix.  defaults
                to 'ns1' if left unspecified.
        '''
        node = self.createAppendElement(namespaceURI, localName, prefix=None)
        node=node._getNode()
        self._setNode(node._getNode())