public function processTemplate($template, $vars = [])
    {
        // override the twig header vars for local resolution
        $this->grav->fireEvent('onTwigTemplateVariables');
        $vars += $this->twig_vars;

        try {
            $output = $this->twig->render($template, $vars);
        } catch (\Twig_Error_Loader $e) {
            throw new \RuntimeException($e->getRawMessage(), 404, $e);
        }

        return $output;

    }