• “All display objects are subclasses of the DisplayObject class… There is no constructor function for the DisplayObject class. You must create another type of object (an object that is a subclass of the DisplayObject type), such as a Sprite, to instantiate an object with the new constructor. Also, if you want to create a custom display object class, you must create a subclass of one of the display object subclasses that has a usable constructor function (such as the Shape class or the Sprite class).”

These “display objects” include Sprite, MovieClip, UIComponent and the Flex Application object.

• “When you instantiate a display object, it will not appear onscreen (on the Stage) until you add the display object instance to a display object container that is on the display list. …When you add any visual element to the Stage, that element becomes a child of the Stage object.”

It is important to remember that the Stage objects inherits from the DisplayObject. This implies that a “child” of the Stage is defined by the DisplayObject. This also implies that any reference to a “display list” most likely refers to the children of the DisplayObject.

The DisplayObject.stage property is read-only. The Flex Application object also also has a stage property (of course).

For more information refer to the “Display Programming” section in “Programming ActionScript 3.0” (Flex 2.01):

http://livedocs.adobe.com/flex/201
    /html/05_Display_Programming_162_01.html