How do I translate createEmptyMovieClip from AS2 to AS3

What would I do to get the same result as this AS2 creation of a box, if I should do it in AS3:

function container(target:MovieClip, boxWidth:Number, boxHeight:Number, cornerRadius:Number, fillColor:Number, fillAlpha:Number):Void {
      with (target) {
            beginFill(fillColor,fillAlpha);
            moveTo(cornerRadius,0);
            lineTo(boxWidth-cornerRadius,0);
            curveTo(boxWidth,0,boxWidth,cornerRadius);
            lineTo(boxWidth,cornerRadius);
            lineTo(boxWidth,boxHeight-cornerRadius);
            curveTo(boxWidth,boxHeight,boxWidth-cornerRadius,boxHeight);
            lineTo(cornerRadius,boxHeight);
            curveTo(0,boxHeight,0,boxHeight-cornerRadius);
            lineTo(0,boxHeight-cornerRadius);
            lineTo(0,cornerRadius);
            curveTo(0,0,cornerRadius,0);
            lineTo(cornerRadius,0);
            endFill();
      }
}
_root.createEmptyMovieClip("factbox", 4);
        factbox._x = zfbX;
        factbox._y = zfbY;

_root.container(factbox, 120, 200, 8, 0xffffff, 100);