code: func isFile(fl FieldLevel) bool {
  	field := fl.Field()
  
  	switch field.Kind() {
  	case reflect.String:
  		fileInfo, err := os.Stat(field.String())
  		if err != nil {
  			return false
  		}
  
  		return !fileInfo.IsDir()
  	}
  
  	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
  }
docs: // IsFile is the validation function for validating if the current field's value is a valid file path.