code: func (i *Index) Chunks(ref string, beg, end int) ([]bgzf.Chunk, error) {
  	id, ok := i.nameMap[ref]
  	if !ok {
  		return nil, index.ErrNoReference
  	}
  	chunks, err := i.idx.Chunks(id, beg, end)
  	if err != nil {
  		return nil, err
  	}
  	return adjacent(chunks), nil
  }
docs: // Chunks returns a []bgzf.Chunk that corresponds to the given genomic interval.