Consider the following:
<!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>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<style type="text/css">
.box-2 { position: absolute }
/* Styling */
.box-1 { background-color: #ccc; width: 3em }
.box-2 { background-color: #ddd; width: 3em }
</style>
</head>
<body>
<table>
<tr>
<td>
<div class="box-1">1</div>
</td>
<td>
<div class="box-2">2</div>
</td>
</tr>
</table>
</body>
</html>
This is rendered as:
Why is box 2 not at the same level than box 1? It has a position: absolute, no top or left, and so I would expect it to be taken out of the normal flow with no impact to its position. (Note that I am not trying to fix a "problem" by changing the CSS, but to understand why browsers render this box this way.)