See documentation for the HTML 4.0 (XHTML) table model.
A container element to hold column descriptions for a table. May describe default behavior for all columns with its attributes.
See documentation for your XML editor or other software to determine the interaction between <colgroup> and <col>.
<!ELEMENT %colgroup.qname; %colgroup.content; >
Table Column (XHTML table model) <col>, zero or more
See documentation for the HTML 4.0 (XHTML) table model.
htmltable.dtd