code: func (fs *FileSorter) Less(i, j int) bool {
  	l := fs.buf[i].key
  	r := fs.buf[j].key
  	ret, err := lessThan(fs.sc, l, r, fs.byDesc)
  	if fs.err == nil {
  		fs.err = err
  	}
  	return ret
  }
docs: // Less implements sort.Interface Less interface.