code: func (w WatchSet) WatchCtx(ctx context.Context) error {
  	if w == nil {
  		return nil
  	}
  
  	if n := len(w); n <= aFew {
  		idx := 0
  		chunk := make([]<-chan struct{}, aFew)
  		for watchCh := range w {
  			chunk[idx] = watchCh
  			idx++
  		}
  		return watchFew(ctx, chunk)
  	}
  
  	return w.watchMany(ctx)
  }
docs: // WatchCtx is used to wait for either the watch set to trigger or for the
  // context to be cancelled. Watch with a timeout channel can be mimicked by
  // creating a context with a deadline. WatchCtx should be preferred over Watch.