code: func handleDirectiveMarker(key string, originalValue, modifiedValue interface{}, patch map[string]interface{}) (bool, error) {
  	if key == directiveMarker {
  		originalString, ok := originalValue.(string)
  		if !ok {
  			return false, fmt.Errorf("invalid value for special key: %s", directiveMarker)
  		}
  		modifiedString, ok := modifiedValue.(string)
  		if !ok {
  			return false, fmt.Errorf("invalid value for special key: %s", directiveMarker)
  		}
  		if modifiedString != originalString {
  			patch[directiveMarker] = modifiedValue
  		}
  		return true, nil
  	}
  	return false, nil
  }
docs: // handleDirectiveMarker handles how to diff directive marker between 2 objects