@Nullable
  public Element serialize(@NotNull ArrangementSectionRule section) {
    final Element sectionElement = new Element(SECTION_ELEMENT_NAME);
    if (StringUtil.isNotEmpty(section.getStartComment())) {
      // or only != null ?
      sectionElement.setAttribute(SECTION_START_ATTRIBUTE, section.getStartComment());
    }
    if (StringUtil.isNotEmpty(section.getEndComment())) {
      sectionElement.setAttribute(SECTION_END_ATTRIBUTE, section.getEndComment());
    }

    //TODO: serialize start & end comment as rule?
    final List<StdArrangementMatchRule> rules = section.getMatchRules();
    for (int i = 0; i < rules.size(); i++) {
      StdArrangementMatchRule rule = rules.get(i);
      if ((i != 0 || StringUtil.isEmpty(section.getStartComment())) &&
          (i != rules.size() - 1 || StringUtil.isEmpty(section.getEndComment()))) {
        sectionElement.addContent(serialize(rule));
      }
    }
    return sectionElement;
   }
@Nullable
  public Element serialize(@NotNull ArrangementSectionRule section)