<!DOCTYPE html>
<html>
<head>
  <meta charset=utf-8>
  <title>&lt;iframe&gt;</title>
</head>
<body>
  <!-- is structured inline -->
  <p><iframe
      src="uri"
      class="class"
      lang="en"></iframe></p>

  <!-- is strictly inline -->
  <p><dfn><iframe
      src="uri"
      class="class"
      lang="en"></iframe></dfn></p>

  <p><dfn>strictly inline
    <iframe>
       text
    </iframe>
  </dfn></p>
  <p>paragraph
    <iframe>
      text
    </iframe>
  </p>
  <p><dfn>strictly inline
    <iframe>
      text
    </iframe>
  </dfn></p>
</body>
</html>