Access to sandbox iframe</h1>
    <script type="text/javascript">
      var t = async_test("Access to sandbox iframe is disallowed")
      var called = 0;
      function calledFromIframe() {
        called++;
      }
      function loaded() {
        t.step(() => {
          assert_throws_dom("SecurityError", () => {
            document.getElementById('sandboxedframe').contentWindow.document;
          });
          assert_equals(called, 0);
          t.done();
        });
      }
    </script>

    <ifram