function quotekey($key, $split=TRUE) {
		$delims=[
			'sqlite2?|mysql'=>'``',
			'pgsql|oci'=>'""',
			'mssql|sqlsrv|odbc|sybase|dblib'=>'[]'
		];
		$use='';
		foreach ($delims as $engine=>$delim)
			if (preg_match('/'.$engine.'/',$this->engine)) {
				$use=$delim;
				break;
			}
		return $use[0].($split ? implode($use[1].'.'.$use[0],explode('.',$key))
			: $key).$use[1];
	}