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

        $timestamp = $helper->render($timestamp);
        $format = $helper->render($format);

        return userdate($timestamp, $format);
    }