code: func (c *engineIPC) ConfigSource(source string) (string, error) {
  	cs := &ipc.ConfigSource{c.ctx, source}
  	if err := c.client.Call("SeesawEngine.ConfigSource", cs, &source); err != nil {
  		return "", err
  	}
  	return source, nil
  }
docs: // ConfigSource requests the configuration source be changed to the
  // specified source. An empty string results in the source remaining
  // unchanged. The current configuration source is returned.