code: func (br *Reader) SetChunk(c *bgzf.Chunk) error {
  	if c != nil {
  		err := br.r.Seek(c.Begin)
  		if err != nil {
  			return err
  		}
  	}
  	br.c = c
  	return nil
  }
docs: // SetChunk sets a limited range of the underlying BGZF file to read, after
  // seeking to the start of the given chunk. It may be used to iterate over
  // a defined genomic interval.