Dispatched when the user moves a pointing device over an InteractiveObject instance.
If the target is a SimpleButton instance, the object displays the overState or upState display object, depending on whether the mouse button is down, as the default behavior.
The onMouseOver event is dispatched each time the mouse enters the area of any child object of the display object container, even if the mouse was already over another child object of the display object container. This is different behavior than the purpose of the onMouseRollOver event, which is to simplify the coding of rollout behaviors for display object containers with children. When the mouse enters the area of a display object or the area of any of its children from an object that is not one of its children, the display object dispatches the rollOver event. The rollOver events are dispatched consecutively down the parent chain of the object.
Source
EventStream<MouseEvent> get onMouseOver => InteractiveObject.mouseOverEvent.forTarget(this);