// https://drafts.csswg.org/css-view-transitions-1/#callbackdef-viewtransitionupdatecallback
callback ViewTransitionUpdateCallback = Promise<any> ();

// https://drafts.csswg.org/css-view-transitions-1/#viewtransition
[Exposed=Window]
interface ViewTransition {
    readonly attribute Promise<undefined> updateCallbackDone;
    readonly attribute Promise<undefined> ready;
    readonly attribute Promise<undefined> finished;
    undefined skipTransition();
};