<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>&lt;m&gt;</title>
</head>
<body>
  <!-- is structured inline -->
  <p><mark class="class" xml:lang="en">text</mark></p>

  <!-- is strictly inline -->
  <p><dfn><mark class="class" xml:lang="en">text</mark></dfn></p>

  <!-- can be empty -->
  <p>text <mark></mark></p>
  <p>text <dfn><mark></mark></dfn></p>

  <!-- can contain interactive -->
  <p><mark><a>text</a></mark></p>
  <p><dfn><mark><a>text</a></mark></dfn></p>

</body>
</html>