code: func (f RegexFormatChecker) IsFormat(input interface{}) bool {
  	asString, ok := input.(string)
  	if !ok {
  		return false
  	}
  
  	if asString == "" {
  		return true
  	}
  	_, err := regexp.Compile(asString)
  	return err == nil
  }
docs: // IsFormat checks if input is a correctly formatted regular expression