code: func (l *Level) Set(v string) error {
  	switch v {
  	case "debug":
  		*l = Debug
  	case "info":
  		*l = Info
  	case "warning":
  		*l = Warning
  	case "error":
  		*l = Error
  
  	default:
  		return errors.New("Unknown log level value.")
  	}
  	return nil
  }
docs: // Set implements flag.Value.