bject.getPrototypeOf(elem), w2.HTMLDivElement.prototype, 'element should be an HTMLDivElement (and not inherited from it)');
  assert_true(errorEvent.error instanceof w.Error, 'error should be an instance created inside the MyElement constructor');
  assert_equals(errorEvent.target, w, `error event should target definition's global but instead targets ${event.target === w2 ? 'document\'s global' : 'test harness global'}`);
}, 'customized built-in: exception thrown in constructor is reported to definition\'s