public static function manifestVersion($manifest) {
        $version = false;
        if (is_array($manifest)) {
            if (isset($manifest[xPDOTransport::MANIFEST_VERSION])) {
                $version = $manifest[xPDOTransport::MANIFEST_VERSION];
            }
            elseif (isset($manifest[xPDOTransport::MANIFEST_VEHICLES])) {
                $version = '0.2';
            }
            else {
                $version = '0.1';
            }
        }
        return $version;
    }