actionscript中this和super的指向问题

package
{
    import flash.display.Sprite;
    
    public class A extends Sprite
    {
        public function A()
        {
            trace(this+":A");
            trace(super+":A");
        }
    }
}

package
{
    public class B extends A
    {
        public function B()
        {
            trace(this+":B");
            trace(super+":B");
        }
    }
}

B是文档类，编译输出：

[object B]:A
[object B]:A
[object B]:B
[object B]:B