code: func validateOptions(data map[string]interface{}, validIndexOptions []string) error {
  	for k, v := range data {
  		switch k {
  		case "options":
  			options, ok := v.(map[string]interface{})
  			if !ok {
  				return errors.New("options is not map[string]interface{}")
  			}
  			for kk, vv := range options {
  				if !foundItem(validIndexOptions, kk) {
  					return fmt.Errorf("unknown key: %v:%v", kk, vv)
  				}
  			}
  		default:
  			return fmt.Errorf("unknown key: %v:%v", k, v)
  		}
  	}
  	return nil
  }
docs: // Raise errors for any unknown key