Why do internal TABLE sections have to go THEAD TFOOT TBODY to validate?
I often use THEAD, TBODY, and TFOOT elements to divide my data tables into sections that can be addressed separately with CSS. I also understand that there is always an implicit TBODY tag.
What puzzles me is the order that these have to go in to validate. THIS table will validate:
<!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" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Table Validation Test</title>
</head>
<body>
<table>
<thead>
<tr>
<th scope="col">Enemies List</th>
</tr>
</thead>
<tfoot>
<tr>
<td>© Bomb Voyage</td>
</tr>
</tfoot>
<tbody>
<tr>
<td>Mr. Incredible</td>
<td>Elastigirl</td>
<td>Gazer Beam</td>
</tr>
</tbody>
</table>
</body>
</html>
But this one will not:
<!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" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Table Validation Test</title>
</head>
<body>
<table>
<thead>
<tr>
<th scope="col">Enemies List</th>
</tr>
</thead>
<tbody>
<tr>
<td>Mr. Incredible</td>
<td>Elastigirl</td>
<td>Gazer Beam</td>
</tr>
</tbody>
<tfoot>
<tr>
<td>© Bomb Voyage</td>
</tr>
</tfoot>
</table>
</body>
</html>
The valid one goes HEAD, FOOT, BODY; which does not make any sense.
Putting the foot at the bottom of the table would maintain the analogy between the table and a human body. But for some reason, this order is considered invalid.
Anyone know why?
Answer
The spec provides a reason:
TFOOT must appear before TBODY within a TABLE definition so that user agents can render the foot before receiving all of the (potentially numerous) rows of data.
http://www.w3.org/TR/html401/struct/tables.html#h-11.2.3
I don't know if any browsers actually follow this behavior, and it was changed in HTML5 to handle both the HTML 4 order and the more logical order:
In this order: optionally a caption element, followed by zero or more colgroup elements, followed optionally by a thead element, followed optionally by a tfoot element, followed by either zero or more tbody elements or one or more tr elements, followed optionally by a tfoot element (but there can only be one tfoot element child in total).