'Add an ``_add_x()`` method to the element class for this child
element.'

def _add_adder(self):

    def _add_child(obj, **attrs):
        new_method = getattr(obj, self._new_method_name)
        child = new_method()
        for (key, value) in attrs.items():
            setattr(child, key, value)
        insert_method = getattr(obj, self._insert_method_name)
        insert_method(child)
        return child
    _add_child.__doc__ = ('Add    a    new    ``<%s>``    child    element    unconditionally,    inserted    in    the    correct    sequence.' % self._nsptagname)
    self._add_to_class(self._add_method_name, _add_child)
