code: func (css separatedString) Minus(css2 separatedString) separatedString {
  	if !sort.StringsAreSorted(css) {
  		sort.Strings(css)
  	}
  	if !sort.StringsAreSorted(css2) {
  		sort.Strings(css2)
  	}
  	k := 0
  	kMax := len(css2)
  	keep := css[:0]
  	for _, s := range css {
  		for k < kMax && css2[k] < s {
  			k++
  		}
  		if k == kMax || css2[k] != s {
  			keep = append(keep, s)
  		}
  	}
  	return keep
  }
docs: // Minus returns a newly created SeparatedString containing all the elements from css that did
  // not appear in css2