Make a rectangle display object?

Question

I currently have some Flash code that adds a rectangle movie clip from my Library ("MaskRectangle") to use as a mask:
private function makeMask(w:Number,h:Number,posX:Number, posY:Number):void {
     var msk:MaskRectangle = new MaskRectangle();
     container.addChild(msk);
     msk.x=posX;
     msk.y=posY;
     msk.width=w;
     msk.height=h;
I would rather generate a Rectangle from code, so I tried:
private function makeMask(w:Number,h:Number,posX:Number, posY:Number):void {
     var msk:Rectangle = new Rectangle(posX,posY,w,h);
     container.addChild(msk);
However, it won't compile because I can't add the Rectangle ("msk") as a child of my "container" sprite, which I create in my constructor function:
//This container will hold all the mask rectangles
container = new Sprite();
//Add the container onto the stage
addChild(container);
//Set the container to be the image's mask
correct_mc.mask=container;
How would I do this?

Answer 1

Because, as I said, I get a compiler error:
1067: Implicit coercion of a value of type flash.geom:Rectangle to an unrelated type flash.display:DisplayObject.
When I try:
private function makeMask(w:Number,h:Number,posX:Number, posY:Number):void {
   var msk:Rectangle = new Rectangle(posX,posY,w,h);
   container.addChild(msk);