code: protected void addClassListing(Content contentTree) {
          Configuration config = configuration;
          if (packageDoc.isIncluded()) {
              addClassKindListing(packageDoc.interfaces(),
                  getResource("doclet.Interfaces"), contentTree);
              addClassKindListing(packageDoc.ordinaryClasses(),
                  getResource("doclet.Classes"), contentTree);
              addClassKindListing(packageDoc.enums(),
                  getResource("doclet.Enums"), contentTree);
              addClassKindListing(packageDoc.exceptions(),
                  getResource("doclet.Exceptions"), contentTree);
              addClassKindListing(packageDoc.errors(),
                  getResource("doclet.Errors"), contentTree);
              addClassKindListing(packageDoc.annotationTypes(),
                  getResource("doclet.AnnotationTypes"), contentTree);
          } else {
              String name = Util.getPackageName(packageDoc);
              addClassKindListing(config.classDocCatalog.interfaces(name),
                  getResource("doclet.Interfaces"), contentTree);
              addClassKindListing(config.classDocCatalog.ordinaryClasses(name),
                  getResource("doclet.Classes"), contentTree);
              addClassKindListing(config.classDocCatalog.enums(name),
                  getResource("doclet.Enums"), contentTree);
              addClassKindListing(config.classDocCatalog.exceptions(name),
                  getResource("doclet.Exceptions"), contentTree);
              addClassKindListing(config.classDocCatalog.errors(name),
                  getResource("doclet.Errors"), contentTree);
              addClassKindListing(config.classDocCatalog.annotationTypes(name),
                  getResource("doclet.AnnotationTypes"), contentTree);
          }
      }
docs: Add class listing for all the classes in this package. 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