code: protected void addClassListing(HtmlTree contentTree) {
          List<PackageElement> packagesIn = ElementFilter.packagesIn(mdle.getEnclosedElements());
          SortedSet<TypeElement> interfaces = new TreeSet<>(utils.makeGeneralPurposeComparator());
          SortedSet<TypeElement> classes = new TreeSet<>(utils.makeGeneralPurposeComparator());
          SortedSet<TypeElement> enums = new TreeSet<>(utils.makeGeneralPurposeComparator());
          SortedSet<TypeElement> exceptions = new TreeSet<>(utils.makeGeneralPurposeComparator());
          SortedSet<TypeElement> errors = new TreeSet<>(utils.makeGeneralPurposeComparator());
          SortedSet<TypeElement> annotationTypes = new TreeSet<>(utils.makeGeneralPurposeComparator());
          for (PackageElement pkg : packagesIn) {
              if (utils.isIncluded(pkg)) {
                  interfaces.addAll(utils.getInterfaces(pkg));
                  classes.addAll(utils.getOrdinaryClasses(pkg));
                  enums.addAll(utils.getEnums(pkg));
                  exceptions.addAll(utils.getExceptions(pkg));
                  errors.addAll(utils.getErrors(pkg));
                  annotationTypes.addAll(utils.getAnnotationTypes(pkg));
              }
          }
          addClassKindListing(interfaces, contents.interfaces, contentTree);
          addClassKindListing(classes, contents.classes, contentTree);
          addClassKindListing(enums, contents.enums, contentTree);
          addClassKindListing(exceptions, contents.exceptions, contentTree);
          addClassKindListing(errors, contents.errors, contentTree);
          addClassKindListing(annotationTypes, contents.annotationTypes, contentTree);
      }
docs: Add class listing for all the classes in this module. Divide class
  listing as per the class kind and generate separate listing for
  Classes, Interfaces, Exceptions and Errors.
  
  @param contentTree the content tree to which the listing will be added