Question

In flex what is the difference between rollover and mouseover?

it occurs first rollover, then mouseover,then mouseout, then rollout.
when these events most suitable?

Answer 1

From the AS3 documentation:

The mouseOver 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 rollOver 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, starting with the highest parent that is neither the root nor an ancestor of the relatedObject and ending with the object.