<!DOCTYPE html>
<!--
Copyright 2022 The Chromium Authors. All rights reserved.
Use of this source code is governed by a BSD-style license that can be
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<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Fullscreen request delegation receiver</title>
</head>
<script>
  // https://wicg.github.io/capability-delegation/spec.html
  async function requestFullscreenAndReport(event) {
    document.documentElement.requestFullscreen().finally(() => {
      event.source.postMessage(!!document.fullscreenElement, "*");
    });
  }

  window.addEventListener("message", requestFullscreenAndReport);
</script>
</html>