docs: def bridge_param(_param, _method, *args, **kwargs):
      """
      Used as a callback to keep the result from the previous callback
      and use that instead of the result of the given callback when
      chaining to the next callback in the fiber.
      """
      assert callable(_method), "method %r is not callable" % (_method, )
      f = Fiber(debug_depth=1, debug_call=_method)
      f.add_callback(drop_param, _method, *args, **kwargs)
      f.add_callback(override_result, _param)
      return f.succeed()