chromium/third_party/blink/web_tests/wpt_internal/fenced_frame/resources/maxframes-inner.html

<!DOCTYPE html>
<script src="utils.js"></script>
<title>Fenced frame content to report whether it loaded</title>

<body>
<script>
function init() {
  // This file is meant to be navigated to from a <fencedframe> element.
  // It reports back to the page hosting the <fencedframe> letting it
  // know that the frame loaded successfully.
  const [window_data_key] = parseKeylist();
  writeValueToServer(window_data_key, "page loaded");
}

init();
</script>
</body>
</html>