When used, this attribute indicates the set of data cells to which the current header cell provides information. The attribute must have one of the valid values. Row; this cell provides header information for the rest of the row that contains it. Col; this cell provides header information for the rest of the column that contains it. Rowgroup; this cell provide information for the rest of the row group that contains it. Colgroup; this cell provide information for the rest of the column group that contains it.