Unusual behavior can be used to collect a group of attributes into a single attribute
package{ import flash.display.Sprite;
public class Main extends Sprite{ public function Main(){
var books:XML = <BOOKS>
<BOOK ISBN="0000000000"/>
<BOOK ISBN="1111111111"/>
<BOOK ISBN="2222222222"/>
</BOOKS>;
var order:XML = <ORDER ITEMS=""/>;
order.@ITEMS = books.*.@ISBN;