public function generateIfMatchHeaderData($data, $allowWeek)
    {
        $result = '';
        // Set an If-Match header if an ETag has been set (version >= 2 only)
        if ($this->_majorProtocolVersion >= 2 &&
                $data instanceof Zend_Gdata_App_Entry) {
            $etag = $data->getEtag();
            if (($etag !== null) &&
                    ($allowWeek || substr($etag, 0, 2) != 'W/')) {
                $result = $data->getEtag();
            }
        }
        return $result;
    }