public function onReady(Container $container)
    {

        /* @var EntryModel $model */
        $model = $container->make($this->getModel());

        if ($model->isVersionable()) {
            $this->setButtons(
                [
                    'versions' => [
                        'href' => 'admin/variables/versions/{entry.id}?group={request.route.parameters.id}',
                    ],
                    'cancel',
                ]
            );
        }
    }