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<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>open</title>
</head>
<body>
  <iframe id="child" src="child.html"></iframe>
  <button id="showdevtools" onclick="showJailedDevTools()">Show Jailed DevTools</button>
  <script>
  function showJailedDevTools() {
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  };
  </script>
</body>
</html>