It's better to show a working example:
The JQuery slider has a functionality I would like to have. When you click on the slider handle and while pressing the mouse button, move the mouse outside the current browser window, the slider handle is still selected. When you release the mouse outside the window, it gets notified and becomes unselected: http://jqueryui.com/demos/slider/
Now I am wondering how a control can be notified when the mouse is released outside the browser window?