code: func MergedEnumerate(ctx context.Context, dest chan<- blob.SizedRef, sources []BlobEnumerator, after string, limit int) error {
  	return mergedEnumerate(ctx, dest, len(sources), func(i int) BlobEnumerator { return sources[i] }, after, limit)
  }
docs: // MergedEnumerate implements the BlobEnumerator interface by
  // merge-joining 0 or more sources.