ttps://dom.spec.whatwg.org/#concept-event-dispatch
  // "14. Unset eventâ€™s [...] stop propagation flag,"
  var e = document.createEvent('Event');
  e.initEvent('foobar', true/*bubbles*/, true/*cancelable*/);
  document.body.addEventListener('foobar', function listener(e) {
    e.stopPropagation();
  });
  document.body.dispatchEvent(e);
  assert_false(e.cancelBubble, "cancelBubble must be false after an event has been dispatched.");
}, "cancelBubble must be false after an event has been dispatched.")