code: func platformSupports(command string) error {
  	if runtime.GOOS != "windows" {
  		return nil
  	}
  	switch command {
  	case "expose", "user", "stopsignal", "arg":
  		return fmt.Errorf("The daemon on this platform does not support the command '%s'", command)
  	}
  	return nil
  }
docs: // platformSupports is a short-term function to give users a quality error
  // message if a Dockerfile uses a command not supported on the platform.