protected function setTemplate(View $view, RootConfig $config)
 {
     $template = $config->getTemplate();
     if (!$template) {
         $template = dirname(dirname(dirname(__DIR__))) . '/templates/main.php';
     }
     if (!file_exists($template) && !is_readable($template)) {
         throw new Exception("Cannot find template '{$template}'.");
     }
     $registry = $view->getViewRegistry();
     $registry->set('__BOOKDOWN__', $template);
     $view->setView('__BOOKDOWN__');
 }