class_docstr: Merge multiple registries of key bindings into one.
  
  This class acts as a proxy to multiple `Registry` objects, but behaves as
  if this is just one bigger `Registry`.
  
  :param registries: List of `Registry` objects.
code: def __init__(self, registries):
      assert all(isinstance(r, BaseRegistry) for r in registries)
  
      _AddRemoveMixin.__init__(self)
  
      self.registries = registries
  
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 1 to create a new MergedRegistry object from inherited base classes: _AddRemoveMixin with example: obj = MergedRegistry(registries)