code: func (i *Index) saveMeta() error {
  	// Marshal metadata.
  	buf, err := proto.Marshal(&internal.IndexMeta{
  		Keys:           i.keys,
  		TrackExistence: i.trackExistence,
  	})
  	if err != nil {
  		return errors.Wrap(err, "marshalling")
  	}
  
  	// Write to meta file.
  	if err := ioutil.WriteFile(filepath.Join(i.path, ".meta"), buf, 0666); err != nil {
  		return errors.Wrap(err, "writing")
  	}
  
  	return nil
  }
docs: // saveMeta writes meta data for the index.