code: func isNumber(fl FieldLevel) bool {
  	switch fl.Field().Kind() {
  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64:
  		return true
  	default:
  		return numberRegex.MatchString(fl.Field().String())
  	}
  }
docs: // IsNumber is the validation function for validating if the current field's value is a valid number.