'Add the appropriate methods to *element_cls*.'

def populate_class_members(self, element_cls, group_prop_name, successors):

    self._element_cls = element_cls
    self._group_prop_name = group_prop_name
    self._successors = successors
    self._add_getter()
    self._add_creator()
    self._add_inserter()
    self._add_adder()
    self._add_get_or_change_to_method()
