docs: void openPageEditor() {
  
          CmsAppWorkplaceUi ui = CmsAppWorkplaceUi.get();
          if (ui.beforeViewChange(new ViewChangeEvent(ui.getNavigator(), ui.getCurrentView(), null, APP_ID, null))) {
              CmsObject cms = A_CmsUI.getCmsObject();
              HttpServletRequest req = CmsVaadinUtils.getRequest();
              if (req == null) {
                  // called from outside the VAADIN UI, not allowed
                  throw new RuntimeException("Wrong usage, this can not be called from outside a VAADIN UI.");
              }
              CmsJspTagEnableAde.removeDirectEditFlagFromSession(req.getSession());
              String page = getPath(cms, req.getSession());
              if (page != null) {
                  A_CmsUI.get().getPage().setLocation(OpenCms.getLinkManager().substituteLink(cms, page));
  
              } else {
                  String message = CmsVaadinUtils.getMessageText(Messages.GUI_PAGE_EDITOR_NOT_AVAILABLE_0);
                  Notification.show(message, Type.WARNING_MESSAGE);
              }
          }
      }