Appearance and Behavior
Events that deserve user attention, but don’t require a response, may be displayed in a Notification Banner. The Banner displays within the user’s field-of-view, but doesn’t block other interaction.
If the user is currently working in a specific screen area, the Banner may be presented in that area. If the Notification is more general, or doesn’t relate to a specific area of the screen, it may be presented in the center of the screen just below the Global Status Bar.
If another Notification Banner is waiting, it appears when the current Banner is dismissed. Banners don’t stack or group.