class_docstr: Common part for ConditionalRegistry and MergedRegistry.
code: def _update_cache(self):
      raise NotImplementedError
  
imports: from __future__ import unicode_literals
  from abc import ABCMeta, abstractmethod
  from prompt_toolkit.cache import SimpleCache
  from prompt_toolkit.filters import CLIFilter, to_cli_filter, Never
  from prompt_toolkit.keys import Key, Keys
  from six import text_type, with_metaclass
label_desc: Use image node_id 2 for calling the _AddRemoveMixin obj's underlying member method code with example usage: obj._update_cache() without return types