#import 
// https://html.spec.whatwg.org/multipage/nav-history-apis.html#popstateevent
[Exposed=Window]
interface PopStateEvent : Event {
    constructor(DOMString type, optional PopStateEventInit eventInitDict = {});
    readonly attribute any state;
    [FIXME] readonly attribute boolean hasUAVisualTransition;
};
dictionary PopStateEventInit : EventInit {
    any state = null;
  // FIXME: boolean hasUAVisualTransition = false;
};