def create(request):
    """
        Called when a node creation request has been received.

        @param request: The publish-subscribe request.
        @type request: L{wokkel.pubsub.PubSubRequest}
        @return: A deferred that fires with a C{unicode} that represents
                 the identifier of the new node.
        @rtype: L{Deferred<twisted.internet.defer.Deferred>}
        """
