code: func (s *Service) KeepFiles(pattern string) error {
  	if len(strings.TrimSpace(pattern)) == 0 {
  		return nil
  	}
  	re, err := regexp.Compile(pattern)
  	if err != nil {
  		return err
  	}
  	s.keepFilesPattern = re
  	return nil
  }
docs: // KeepFiles sets a regex pattern of remote public ids that won't be deleted
  // by any Delete() command. This can be useful to forbid deletion of some
  // remote resources. This regexp pattern applies to both image and raw data
  // types.