code: def super(self, name, current):
          
          try:
              blocks = self.blocks[name]
              index = blocks.index(current) + 1
              blocks[index]
          except LookupError:
              return self.environment.undefined('there is no parent block '
                                                'called %r.' % name,
                                                name='super')
          return BlockReference(name, self, blocks, index)
docs: Render a parent block.