Jeff dePascale Blogging on and developing web and mobile technologies

MouseEvent – relatedObject explained

One of those things that isn't immediately clear based on its name, the relatedObject property is a reference to the object that the mouse is now over, and is receiving a MouseEvent.MOUSE_OVER event.  This property is valid for both over and out events. This is a really useful property, a typical example is working with mutually exclusive rollovers. if you have a rollover popup that should remain visible if the users cursor rolls into the popup itself, you need to case your mouseOut to only hide the popup if the cursor is not over the popup itself. Here is an example: