code: func (f IPV4FormatChecker) IsFormat(input interface{}) bool {
  	asString, ok := input.(string)
  	if !ok {
  		return false
  	}
  
  	// Credit: https://github.com/asaskevich/govalidator
  	ip := net.ParseIP(asString)
  	return ip != nil && strings.Contains(asString, ".")
  }
docs: // IsFormat checks if input is a correctly formatted IPv4-address