Hyper Text Markup Language (HTML) Question: Download HTML PDF

Yes, a table can be embedded inside a cell in another table. Here's a simple example:

<table>
<tr>
<td>this is the first cell of the outer table</td>
<td>this is the second cell of the outer table,

with the inner table embedded in it
<table>
<tr>
<td>this is the first cell of the inner table</td>
<td>this is the second cell of the inner table</td>
</tr>
</table>
</td>
</tr>
</table>

The main caveat about nested tables is that older versions of Netscape Navigator have problems with them if you don't explicitly close your TR, TD, and TH elements. To avoid problems, include every </tr>, </td>, and </th> tag, even though the HTML specifications don't require them.
Also, older versions of Netscape Navigator have problems with tables that are nested extremely deeply (e.g., tables nested ten deep). To avoid problems, avoid nesting tables more than a few deep. You may be able to use the ROWSPAN and COLSPAN attributes to minimize table nesting.
Finally, be especially sure to validate your markup whenever you use nested tables.