code: def RegisterPlugin(cls, plugin_class):
      
      plugin_name = plugin_class.NAME.lower()
      if plugin_name in cls._plugin_classes:
        raise KeyError((
            'Plugin class already set for name: {0:s}.').format(
                plugin_class.NAME))
  
      cls._plugin_classes[plugin_name] = plugin_class
docs: Registers a plugin class.
  
      The plugin classes are identified based on their lower case name.
  
      Args:
        plugin_class (type): class of the plugin.
  
      Raises:
        KeyError: if plugin class is already set for the corresponding name.