code: public Content getPackageSerializedHeader() {
          HtmlTree htmlTree;
          if (configuration.allowTag(HtmlTag.SECTION)) {
              htmlTree = HtmlTree.SECTION();
          } else {
              htmlTree = new HtmlTree(HtmlTag.LI);
              htmlTree.addStyle(HtmlStyle.blockList);
          }
          return htmlTree;
      }
docs: Get the package serialized form header.
  
  @return the package serialized form header tree