code: func (f DateFormatChecker) IsFormat(input interface{}) bool {
  	asString, ok := input.(string)
  	if !ok {
  		return false
  	}
  	_, err := time.Parse("2006-01-02", asString)
  	return err == nil
  }
docs: // IsFormat checks if input is a correctly formatted  date (YYYY-MM-DD)