code: def overextends(parser, token):
      
      bits = token.split_contents()
      if len(bits) != 2:
          raise TemplateSyntaxError("'%s' takes one argument" % bits[0])
      parent_name = parser.compile_filter(bits[1])
      nodelist = parser.parse()
      if nodelist.get_nodes_by_type(ExtendsNode):
          raise TemplateSyntaxError("'%s' cannot appear more than once "
                                    "in the same template" % bits[0])
      return OverExtendsNode(nodelist, parent_name, None)
docs: Extended version of Django's ``extends`` tag that allows circular
      inheritance to occur, eg a template can both be overridden and
      extended at once.