[Exposed=Window]
interface HTMLPersistentWidgetElement : HTMLElement {
  [Reflect, URL, CEReactions] attribute USVString src;
  [Reflect, CEReactions] attribute DOMString name;
  undefined postMessage(any message, USVString targetOrigin);
  undefined postMessage(any message, optional WindowPostMessageOptions options = {});
};

[Exposed=Window]
interface PersistentWidgetOpener : EventTarget {
  undefined postMessage(any message, USVString targetOrigin);
  undefined postMessage(any message, optional WindowPostMessageOptions options = {});
};

partial interface Window {
  [SameObject] readonly attribute PersistentWidgetOpener? persistentWidgetOpener;
};

partial interface mixin WindowEventHandlers {
  attribute EventHandler onopenerchange;
};