code: func (r *Reader) LabelIndices() ([][]string, error) {
  	var res [][]string
  	for s := range r.labels {
  		res = append(res, strings.Split(s, labelNameSeperator))
  	}
  	return res, nil
  }
docs: // LabelIndices returns a slice of label names for which labels or label tuples value indices exist.
  // NOTE: This is deprecated. Use `LabelNames()` instead.