code: func (he *hashExplorer) Put(ctx context.Context, chunkData ChunkData) (Reference, error) {
  	// Need to do the actual Put, which returns the references
  	ref, err := he.hasherStore.Put(ctx, chunkData)
  	if err != nil {
  		return nil, err
  	}
  	// internally store the reference
  	he.lock.Lock()
  	he.references = append(he.references, ref)
  	he.lock.Unlock()
  	return ref, nil
  }
docs: // HashExplorer's Put will add just the chunk hashes to its `References`