#import 
#import 
// FIXME: typedef (WindowProxy or MessagePort or ServiceWorker) MessageEventSource;
typedef (WindowProxy or MessagePort) MessageEventSource;
// https://html.spec.whatwg.org/multipage/comms.html#messageevent
[Exposed=(Window,Worker)]
interface MessageEvent : Event {
    constructor(DOMString type, optional MessageEventInit eventInitDict = {});
    readonly attribute any data;
    readonly attribute USVString origin;
    readonly attribute DOMString lastEventId;
    readonly attribute MessageEventSource? source;
    // FIXME: readonly attribute FrozenArray ports;
    readonly attribute any ports;
};
dictionary MessageEventInit : EventInit {
    any data = null;
    USVString origin = "";
    DOMString lastEventId = "";
    MessageEventSource? source = null;
    // FIXME: sequence ports = [];
    sequence