ladybird/Libraries/LibWeb/HTML/MessagePort.idl

// https://html.spec.whatwg.org/multipage/web-messaging.html#messageport
[Exposed=(Window,Worker,AudioWorklet), Transferable]
interface MessagePort : EventTarget {
    undefined postMessage(any message, sequence<object> transfer);
    undefined postMessage(any message, optional StructuredSerializeOptions options = {});
    undefined start();
    undefined close();

    // event handlers
    attribute EventHandler onmessage;
    attribute EventHandler onmessageerror;
};

dictionary StructuredSerializeOptions {
    sequence<object> transfer = [];
};