@classmethod
def set_default_renderer(cls, renderer):
    """ Set the callable that will act as a default renderer for
        instances of the associated class when no ``renderer``
        argument is provided to the class' constructor.  Useful when
        you'd like to use an alternate templating system.

        Calling this method resets the :term:`default renderer`.
        """
    cls.default_renderer = staticmethod(renderer)
