code: def _append_node(self, child):
          
          # pylint: disable=no-member; depending by the class
          # which uses the current class as a mixin or base class.
          # It's rewritten in 2.0, so it makes no sense for now
          # to spend development time on it.
          self.body.append(child)
          child.parent = self
docs: append a child, linking it in the tree