code: public static void generate(ConfigurationImpl configuration, PackageElement packageElement)
              throws DocFileIOException {
          PackageFrameWriter packgen = new PackageFrameWriter(configuration, packageElement);
          String pkgName = configuration.utils.getPackageName(packageElement);
          HtmlTree body = packgen.getBody(false, packgen.getWindowTitle(pkgName));
          Content pkgNameContent = new StringContent(pkgName);
          HtmlTree htmlTree = (configuration.allowTag(HtmlTag.MAIN))
                  ? HtmlTree.MAIN()
                  : body;
          Content heading = HtmlTree.HEADING(HtmlConstants.TITLE_HEADING, HtmlStyle.bar,
                  packgen.getTargetPackageLink(packageElement, "classFrame", pkgNameContent));
          htmlTree.addContent(heading);
          HtmlTree div = new HtmlTree(HtmlTag.DIV);
          div.addStyle(HtmlStyle.indexContainer);
          packgen.addClassListing(div);
          htmlTree.addContent(div);
          if (configuration.allowTag(HtmlTag.MAIN)) {
              body.addContent(htmlTree);
          }
          packgen.printHtmlDocument(
                  configuration.metakeywords.getMetaKeywords(packageElement), false, body);
      }
docs: Generate a package summary page for the left-hand bottom frame. Construct
  the PackageFrameWriter object and then uses it generate the file.
  
  @param configuration the current configuration of the doclet.
  @param packageElement The package for which "pacakge-frame.html" is to be generated.
  @throws DocFileIOException if there is a problem generating the package summary page