HTML (since at least HTML 4.01) supports a ‘scope’ attribute for cells to which a header cell applies. The HTML 5 markup for the table is shown below:

  <caption>Measurement of legs and tails in Cats and English
    <tr> <th> ID <th> Measurement <th> Average <th> Maximum
    <tr> <td> <th scope=rowgroup> Cats <td> <td>
    <tr> <td> 93 <th scope=row> Legs <td> 3.5 <td> 4
    <tr> <td> 10 <th scope=row> Tails <td> 1 <td> 1
    <tr> <td> <th scope=rowgroup> English speakers <td> <td>
    <tr> <td> 32 <th scope=row> Legs <td> 2.67 <td> 4
    <tr> <td> 35 <th scope=row> Tails <td> 0.33 <td> 1

HTML also supports a ‘headers’ attribute for indicating the header cell or cells that apply to the current cell.