content. It includes an optional backdrop, and can be used to implement a variety
of UI controls including dialogs and drop downs. Multiple overlays may be displayed at once.

### Closing and canceling

A dialog may be hidden by closing or canceling. The difference between close and cancel is user
intent. Closing generally implies that the user acknowledged the content on the overlay. By default,
it will cancel whenever the user taps outside it or presses the escape key. This behavior is
configurable with t