
<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
  </head>
  <body>
    <iframe sandbox="allow-scripts"></iframe>
    <script>
      let frame = document.querySelector("iframe");
      let sandbox = new URL(location.href).searchParams.get("sandbox");
      if (sandbox) {
        frame.sandbox = sandbox;
      }
      // We're the popup (i.e. a top frame).  Load into the iframe the page
      // trying to modifying the top frame and transmit the result to our
      // opener.
      onmessage = fun