code: func (c Calendar) formatDateTimeComponentHour12(datetime time.Time, length int) (string, error) {
  	hour := datetime.Hour()
  	if hour > 12 {
  		hour = hour - 12
  	}
  
  	switch length {
  	case datetimeFormatLength1Plus:
  		return fmt.Sprintf("%d", hour), nil
  	case datetimeFormatLength2Plus:
  		if hour < 10 {
  			return fmt.Sprintf("0%d", hour), nil
  		}
  		return fmt.Sprintf("%d", hour), nil
  	}
  
  	return "", fmt.Errorf("unsupported hour-12: %d", length)
  }
docs: // formatDateTimeComponentHour12 renders an hour-component using a 12-hour
  // clock.