code: def AddSubkey(self, registry_key):
      
      name = registry_key.name.upper()
      if name in self._subkeys:
        raise KeyError(
            'Subkey: {0:s} already exists.'.format(registry_key.name))
  
      self._subkeys[name] = registry_key
  
      key_path = key_paths.JoinKeyPath([self._key_path, registry_key.name])
      registry_key._key_path = key_path
docs: Adds a subkey.
  
      Args:
        registry_key (WinRegistryKey): Windows Registry subkey.
  
      Raises:
        KeyError: if the subkey already exists.