HTML5 validity of nested tables
This document, which contains nothing but a nested table:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>A nested table</title>
</head>
<body>
<table>
<tbody>
<tr>
<td>
<table>
<tbody>
<tr>
<td>Nested</td>
<td>Table</td>
</tr>
</tbody>
</table>
</td>
</tr>
</tbody>
</table>
</body>
</html>
…is valid, according to http://validator.w3.org/nu/:
The document validates according to the specified schema(s) and to additional constraints checked by the validator.