protected static function getResponseFormat()
    {
        // Check content type
        foreach (headers_list() as $header) {
            if (stripos($header, 'content-type:') === 0) {
                // This handler only works with HTML and javascript outputs
                // text/javascript is obsolete in favour of application/javascript, but still used
                if (stripos($header, 'application/javascript') !== false || stripos($header, 'text/javascript') !== false) {
                    return 'js';
                }
                if (stripos($header, 'text/html') === false) {
                    return 'unknown';
                }
                break;
            }
        }

        return 'html';
    }