Dynamic Table

Hello,

I have a very basic XML document that looks like:
<domain>
  <variable> abc </variable>
  <variable> def </variable>
  <variable> ghi </variable>
  <variable> abcdefgh </variable>
  <variable> abcdef </variable>
  <variable> abc </variable>
  ...
</domain>

And I would like to create an HTML table with, for example, 3 columns. Each
column can contain 3 characters max. The result of my transformation should
look like:
<table>
  <tr>
    <td> abc </td>
    <td> def </td>
    <td> def </td>
  </tr>
  <tr>
    <td colspan = "3"> abcdefgh </td>
  </tr>
  <tr>
    <td colspan = "2"> abcdef </td>
    <td> abc </td>
  </tr>
</table>

I don't have a clue how to dynamically determine the colspan attribute and
start a new row if there is not enough room to put the content of a variable.

Many thanks in advance for your help,
Frangois