3D Full Screen Mode
The 
button creates a new 3D view in full screen mode. In this view you can also open the properties dialog or edit an object, e.g. a window, with a double click. But unlike normal 3D views, the selection of an object is not cancelled with ‘Esc’, since ‘Esc’, just like the 
button, is used to terminate full screen mode. In this case, if you want to cancel the selection of an object, you have to click in an empty area of the scene.