This event is emitted before a layer is dismissed.
The event is emitted on the element of the layer that is about to close.
Closing overlays
The layer that is about to close.
The overlay's dismissal value.
Listeners may replace or mutate this value.
The element that is causing the layer to close.
Will be undefined if the overlay is not closing by a user interacting with an element.
undefined
The server response that is causing this overlay to close.
Will be undefined if the overlay is not closing in reaction to a server response.
See Using the discarded response.
Event listeners may call this method to prevent the overlay from closing.
