code: public long getDiffId() {
      Matcher matcher = DIFF_ID_PATTERN.matcher(id);
      if (matcher.find()) {
        return Long.parseLong(matcher.group(1));
      } else {
        // newly created article
        return 0;
      }
    }
docs: Get the diff id from the 'id' element, or {@code 0} if the diff is the creation of a new article.