public function begin_database_export($version, $release, $timestamp, $description) {
        $this->output('<?xml version="1.0" encoding="utf-8"?>');
        //TODO add xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" and schema information
        $this->output('<moodle_database version="'.$version.'" release="'.$release.'" timestamp="'.$timestamp.'"'.(empty ($description) ? '' : ' comment="'.htmlspecialchars($description, ENT_QUOTES, 'UTF-8').'"').'>');
    }