public static function diffUndo(array $args, array $named)
 {
     if (count($args) !== 1) {
         throw new WrongNumberArgumentsException($args, 'one');
     }
     list($diffContent) = $args;
     $differenceEngine = new \DifferenceEngine();
     $multi = $differenceEngine->getMultiNotice();
     $notice = '';
     if ($diffContent === '') {
         $notice = '<div class="mw-diff-empty">' . wfMessage('diff-empty')->parse() . "</div>\n";
     }
     $differenceEngine->showDiffStyle();
     return self::html($differenceEngine->addHeader($diffContent, wfMessage('flow-undo-latest-revision'), wfMessage('flow-undo-your-text'), $multi, $notice));
 }