public function shorten($args, Mustache_LambdaHelper $helper) {
        // Split the text into an array of variables.
        list($length, $text) = explode(',', $args, 2);
        $length = trim($length);
        $text = trim($text);

        // Allow mustache tags in the text.
        $text = $helper->render($text);

        return shorten_text($text, $length);
    }