http://www.w3.org/1999/xhtml
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<style type="text/css">
table { height:100%;background:yellow; }
</style>
</head>
<body>
<table>
<tbody>
<tr><td>How tall is this?</td></tr>
</tbody>
</table>
</body>
</html>