code: func looksInternal(tok string) bool {
  	internal := []string{")", `’`, `”`, `"`, `'`}
  	for _, punc := range internal {
  		if strings.HasSuffix(tok, punc) {
  			return true
  		}
  	}
  	return false
  }
docs: // looksInternal determines if tok's punctuation could appear
  // sentence-internally (i.e., parentheses or quotations).