code: def is_cached(self, link):
          '''Returns whether the current navigator is cached. Intended
          to be overwritten and customized by subclasses.
          '''
          if link is None:
              return False
          elif hasattr(link, 'uri'):
              return link.uri in self.id_map
          else:
              return link in self.id_maf is_cached(self, link):
          '''Returns whether the current navigator is cached. Intended
          to be overwritten and customized by subclasses.
          '''
          if link is None:
              return False
          elif hasattr(link, 'uri'):
              return link.uri in self.id_map
          else:
              return link in self.id_map
docs: Returns whether the current navigator is cached. Intended
          to be overwritten and customized by subclasses.