code: func (i *Index) MatchTagValueSeriesIDIterator(name, key []byte, value *regexp.Regexp, matches bool) (tsdb.SeriesIDIterator, error) {
  	release := i.sfile.Retain()
  	defer release()
  
  	itr, err := i.matchTagValueSeriesIDIterator(name, key, value, matches)
  	if err != nil {
  		return nil, err
  	}
  	return tsdb.FilterUndeletedSeriesIDIterator(i.sfile, itr), nil
  }
docs: // MatchTagValueSeriesIDIterator returns a series iterator for tags which match value.
  // If matches is false, returns iterators which do not match value.