code: protected void addClassKindListing(ClassDoc[] arr, Content labelContent,
              HtmlTree contentTree) {
          arr = utils.filterOutPrivateClasses(arr, configuration.javafx);
          if(arr.length > 0) {
              Arrays.sort(arr);
              boolean printedHeader = false;
              HtmlTree htmlTree = (configuration.allowTag(HtmlTag.SECTION))
                      ? HtmlTree.SECTION()
                      : contentTree;
              HtmlTree ul = new HtmlTree(HtmlTag.UL);
              ul.setTitle(labelContent);
              for (ClassDoc classDoc : arr) {
                  if (documentedClasses != null && !documentedClasses.contains(classDoc)) {
                      continue;
                  }
                  if (!utils.isCoreClass(classDoc) || !configuration.isGeneratedDoc(classDoc)) {
                      continue;
                  }
                  if (!printedHeader) {
                      Content heading = HtmlTree.HEADING(HtmlConstants.CONTENT_HEADING,
                                                         true, labelContent);
                      htmlTree.addContent(heading);
                      printedHeader = true;
                  }
                  Content arr_i_name = new StringContent(classDoc.name());
                  if (classDoc.isInterface())
                      arr_i_name = HtmlTree.SPAN(HtmlStyle.interfaceName, arr_i_name);
                  Content link = getLink(new LinkInfoImpl(configuration,
                                                          LinkInfoImpl.Kind.PACKAGE_FRAME, classDoc).label(arr_i_name).target("classFrame"));
                  Content li = HtmlTree.LI(link);
                  ul.addContent(li);
              }
              htmlTree.addContent(ul);
              if (configuration.allowTag(HtmlTag.SECTION)) {
                  contentTree.addContent(htmlTree);
              }
          }
      }
docs: Add specific class kind listing. Also add label to the listing.
  
  @param arr Array of specific class kinds, namely Class or Interface or Exception or Error
  @param labelContent content tree of the label to be added
  @param contentTree the content tree to which the class kind listing will be added