code: func (f *Field) saveMeta() error {
  	// Marshal metadata.
  	fo := f.options
  	buf, err := proto.Marshal(fo.encode())
  	if err != nil {
  		return errors.Wrap(err, "marshaling")
  	}
  
  	// Write to meta file.
  	if err := ioutil.WriteFile(filepath.Join(f.path, ".meta"), buf, 0666); err != nil {
  		return errors.Wrap(err, "writing meta")
  	}
  
  	return nil
  }
docs: // saveMeta writes meta data for the field.