code: def extra(name: str, desc: str) -> Callable:
      
  
      def attr_dec(f):
          f.__setattr__("extra_fn", True)
          f.__setattr__("name", name)
          f.__setattr__("desc", desc)
          return f
  
      return attr_dec
docs: Decorator for slave channel's "additional features" interface.
  
      Args:
          name (str): A human readable name for the function.
          desc (str): A short description and usage of it. Use
              ``{function_name}`` in place of the function name
              in the description.
  
      Returns:
          The decorated method.