docs: final public void addOffset(Integer start, Integer end) {
      if (tokenOffset == null) {
        setOffset(start, end);
      } else if ((start == null) || (end == null)) {
        // do nothing
      } else if (start > end) {
        throw new IllegalArgumentException("Start offset after end offset");
      } else {
        tokenOffset.add(start, end);
      }
    }