See documentation for the HTML 4.0 (XHTML) table model.
The description of one column of a table
<!ELEMENT %col.qname; %col.content; >
This is an EMPTY element
<colgroup> Table Column Group (XHTML table model); <table> Table (XHTML table model)
... <table-wrap id="TX0.180"> <caption><p>Patient costs for institutional care at the end of scheduled follow up</p></caption> <table border="1"> <colgroup> <col span="1"/> <col align="char" char="," charoff="50%" span="1"/> </colgroup> <thead> <tr> <th>Year</th> <th>Cost per patient</th> </tr> </thead> <tbody> <tr> <td>1997</td> <td>$8,250</td> </tr> <tr> <td>2000</td> <td>$31,400</td> </tr> <tr> <td>2003</td> <td>$125,600</td> </tr> </tbody> </table> </table-wrap> ...
htmltable.dtd