Once upon a time public class He { ... } <b>met she</b> public class He { ... private var girl731:She; } <b>someday</b> public class He { ... this.girlfriend = girl731 as Girlfriend; } <b>one night</b> public class He { ... this.girlfriend.addChild( this.clone() ); } <b>because</b> public class She extends DisplayObjectContainer { ... }

The DisplayObjectContainer is a subclass of the DisplayObject that can contain multiple DisplayObject's. For add some of them need to call a method DisplayObjectContainer.addChild(myDisplayObject).