me = form.previousSibling;
  iframe.onload = t1.step_func(() => {
    // The initial about:blank load event can be fired before the form navigation occurs.
    // See https://github.com/whatwg/html/issues/490 for more information.
    if (iframe.contentWindow.location.href == "about:blank") { return; }
    assert_true(iframe.contentWindow.location.search.indexOf('n1=v1&h1=vh1') != -1);
    t1.done();
  });
  form.submit();
});

test(() => {
  const form = populateForm('');
  form.addEventListener('formdata'