code: @Override
      @SuppressWarnings("checkstyle:illegalcatch")
      public void onClick(final AjaxRequestTarget _target)
      {
          Instance instance = null;
          try {
              if (this.target.equals(ScriptTarget.TOP)) {
                  final PageReference reference = ((AbstractContentPage) getPage()).getCalledByPageReference();
                  if (reference != null) {
                      final UIMenuItem menuItem = (UIMenuItem) ((ContentContainerPage) reference.getPage()).getMenuTree()
                                      .getSelected().getDefaultModelObject();
                      final RecentObjectLink link = new RecentObjectLink(menuItem);
                      if (link != null) {
                          ((EFapsSession) getSession()).addRecent(link);
                      }
                  }
              }
              final AbstractUIField uiField = super.getModelObject();
              if (uiField.getInstanceKey() != null) {
                  Menu menu = null;
                  try {
                      instance = uiField.getInstance();
                      menu = Menu.getTypeTreeMenu(instance.getType());
                  } catch (final Exception e) {
                      if (menu == null) {
                          throw new EFapsException(LoadInTargetAjaxLink.class, "NoTreeMenu", instance);
                      }
                  }
  
                  final ContentContainerPage page = new ContentContainerPage(menu.getUUID(), uiField.getInstanceKey(),
                                  uiField.getParent() instanceof UIStructurBrowser);
                  final CharSequence url = urlFor(new RenderPageRequestHandler(new PageProvider(page)));
                  // touch the page to ensure that the pagemanager stores it to be accessible
                  getSession().getPageManager().touchPage(page);
                  final StringBuilder js = new StringBuilder()
                      .append(this.target.key).append(".dijit.registry.byId(\"").append("mainPanel")
                      .append("\").set(\"content\", dojo.create(\"iframe\",{")
                      .append("\"id\": \"").append(MainPage.IFRAME_ID)
                      .append("\",\"src\": \"./wicket/").append(url)
                      .append("\",\"style\": \"border: 0; width: 100%; height: 99%\"")
                      .append("}));");
                  _target.appendJavaScript(js);
              }
          } catch (final EFapsException e) {
              throw new RestartResponseException(new ErrorPage(e));
          }
      }
docs: Method to load something inside the opener window.
  
  @param _target AjaxRequestTarget