code: func (s *Sanitizer) NewWatcher(ctx context.Context, watch Watch) (Watcher, error) {
  	for _, prefix := range watch.Prefixes {
  		if !isKeySafe(prefix) {
  			return nil, trace.BadParameter(errorMessage)
  		}
  	}
  	return s.backend.NewWatcher(ctx, watch)
  }
docs: // NewWatcher returns a new event watcher