Take for instance this XHTML snippet:

```
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
  <title>A webpage</title>
</head>
<body>
  <p>
    <form action="something.php" method="get">
      <input type="submit" value="Hello"/>
    </form>
  </p>
</body>
</html>

```

The tree should be valid, however this won't parse correctly in a browser.