$flashMessage = t3lib_div::makeInstance(
        't3lib_FlashMessage',
        'message',
        'title',
        t3lib_FlashMessage::INFO
);
$content .= $flashMessage->render();

t3lib_FlashMessage::NOTICE
t3lib_FlashMessage::INFO
t3lib_FlashMessage::OK
t3lib_FlashMessage::WARNING
t3lib_FlashMessage::ERROR