protected function _generateSearchText(...$contentParts)
    {
        $searchText = '';
        foreach ($contentParts as $contentPart) {
            $contentPart = trim((string) $contentPart);
            if ($contentPart !== '') {
                $searchText .= $contentPart . ' ';
            }
        }
        $searchText = trim(strip_tags($searchText));
        return ($searchText !== '') ? $searchText : null;
    }