submit" value="true">submit</button>
</form>

<script>

const form1 = document.getElementById('form1'),
      form2 = document.getElementById('form2'),
      frame1 = document.getElementById('frame1'),
      frame2 = document.getElementById('frame2');

test(() => {
  const formData = new FormData(form1);
  assert_equals(formData.get('_charset_'), 'UTF-8');
}, 'FormData constructor always produces UTF-8 _charset_ value.');

async_test(t => {
  frame1.onload = t.step_func(() => {
    if (frame1.contentWindow.