code: func (i *Index) Add(r Record, c bgzf.Chunk, placed, mapped bool) error {
  	refName := r.RefName()
  	rid, ok := i.nameMap[refName]
  	if !ok {
  		rid = len(i.refNames)
  		i.refNames = append(i.refNames, refName)
  	}
  	shim := tabixShim{id: rid, start: r.Start(), end: r.End()}
  	return i.idx.Add(shim, internal.BinFor(r.Start(), r.End()), c, placed, mapped)
  }
docs: // Add records the SAM record as having being located at the given chunk.