code: 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()
docs: Add the appropriate methods to *element_cls*.