reateElement('div', {is: 'my-div'});
  let errorEvent = await nextErrorPromise;
  assert_equals(Object.getPrototypeOf(elem), w2.HTMLDivElement.prototype, 'element should be an HTMLDivElement (and not inherited from it)');
  assert_equals(errorEvent.target, w, `error event should target definition's global but instead targets ${event.currentTarget === w2 ? 'document\'s global' : 'test harness global'}`);
}, 'customized built-in: exception thrown by spec due to not returning the same value is reported to defi