code: private void addClassFrameTag(Content contentTree) {
          HtmlTree frame = HtmlTree.IFRAME(configuration.topFile.getPath(), "classFrame",
                  configuration.getText("doclet.Package_class_and_interface_descriptions"));
          frame.addStyle(HtmlStyle.rightIframe);
          contentTree.addContent(frame);
      }
docs: Add the IFRAME tag for the frame that describes the class in detail.
  
  @param contentTree the content tree to which the information will be added