chromium/chrome/test/data/extensions/api_test/automation/sites/fencedframe/fencedframe_outer.html

<!--
* Copyright 2022 The Chromium Authors
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
-->
<body>
  <fencedframe></fencedframe>
  <script>
    const url = new URL("/fencedframe/fencedframe_inner.html", location.href);
    document.querySelector("fencedframe").config = new FencedFrameConfig(url);
  </script>
  <p>outer end</p>
</body>