code: private void addAllPackagesFrameTag(Content contentTree) {
          HtmlTree frame = HtmlTree.IFRAME(DocPaths.OVERVIEW_FRAME.getPath(),
                  "packageListFrame", configuration.getText("doclet.All_Packages"));
          HtmlTree leftTop = HtmlTree.DIV(HtmlStyle.leftTop, frame);
          contentTree.addContent(leftTop);
      }
docs: Add the IFRAME tag for the frame that lists all packages.
  
  @param contentTree the content tree to which the information will be added