Listing 21.6. Dokument index.html z ćwiczenia 21.6
<!DOCTYPE html>
<html>
  <head>
    <title>Ćwiczenie 20.6</title>
    <meta charset="UTF-8" />
    <style>
    iframe {
        width: 800px;
        height: 600px;
    }
    </style>
  </head>
<body>

<iframe src="next-level.html"></iframe>

</body>
</html>