docs: def _add_public_adder(self):
          """
          Add a public ``add_x()`` method to the parent element class.
          """
          def add_child(obj):
              private_add_method = getattr(obj, self._add_method_name)
              child = private_add_method()
              return child
  
          add_child.__doc__ = (
              'Add a new ``<%s>`` child element unconditionally, inserted in t'
              'he correct sequence.' % self._nsptagname
          )
          self._add_to_class(self._public_add_method_name, add_child)