code: def _link_for_value(self, value):
      '''Returns the linked key if `value` is a link, or None.'''
      try:
        key = Key(value)
        if key.name == self.sentinel:
          return key.parent
      except:
        pass
      return Nonf _link_for_value(self, value):
      '''Returns the linked key if `value` is a link, or None.'''
      try:
        key = Key(value)
        if key.name == self.sentinel:
          return key.parent
      except:
        pass
      return None
docs: Returns the linked key if `value` is a link, or None.