code: func indexFragment(s string) int {
  	max := -1
  	for _, sep := range []string{". ", ": ", "; ", ", ", "! ", "? ", "\" ", "' "} {
  		if idx := strings.LastIndex(s, sep); idx > max {
  			max = idx
  		}
  	}
  	if max > 0 {
  		return max + 2
  	}
  	if idx := strings.LastIndex(s, " "); idx > 0 {
  		return idx + 1
  	}
  	return -1
  }
docs: // indexFragment looks for the last sentence split-point (defined as one of
  // the punctuation characters .:;,!?"' followed by a space) in the string s
  // and returns the index in the string after that split-point. If no split-
  // point is found it returns the index after the last space in s, or -1.