Use the scope attribute on table cells used as a header.
In HTML5 the scope attribute is allowed only on
<th> elements. scope= colgroup can be used on
<th> element only if it has a colspan attribute. scope= rowgroup can be used on
<th> element only if it has a rowspan attribute.
The scope attribute should be used to clarify the scope of any cell used as a header. The scope identifies whether the cell is a header for a row, column, or group of rows or columns.