All cells in a table element that use the headers attribute must only refer to other cells of that same table

Screen readers have a specific way of announcing tables. When tables are not properly marked up, this creates the opportunity for confusing or inaccurate screen reader output.

Sighted users can usually tell at a glance what the table's headers are and what their relationship to the data is. For non-sighted users this must be done in the markup.

When a data table is designed with accessibility in mind, the user enters into table navigation mode, which allows the user to navigate from cell to cell within the table while hearing the screen reader announce the corresponding table headers for the data cells. Hearing the table headers is especially helpful when navigating through large data tables, or when cells contain similar-sounding data that could be easily confused.

Table navigation mode is not useful, though, if the table lacks accessibility features.

Fixing the problem

To fix the problem, ensure that each cell in a table using headers refers to another cell in the same table by creating a scope attribute value on each th element within tr elements. This rule checks that references to header columns and rows connect to specific td elements.

The scope attribute tells the browser and screen reader that everything under the column is related to the header at the top, and everything to the right of the row header is related to that header.

Applying the scope attribute to our table the markup now looks like this:

example" idid81_example_scope_attribute">

Example

<table>
<caption><strong>Greensprings Running Club Personal Bests</strong></caption>
<thead>
<tr>  <th scope="col">Name</th>  <th scope="col">1 mile</th>  <th scope="col">5 km</th>  <th scope="col">10 km</th>
</tr>
</thead>
<tbody>
<tr>  <th scope="row">Mary</th>
<td>8:32</td>
<td>28:04</td>
<td>1:01:16</td>
</tr>
<tr>  <th scope="row">Betsy</th>
<td>7:43</td>
<td>26:47</td>
<td>55:38</td>
</tr>
<tr>  <th scope="row">Matt</th>
<td>7:55</td>
<td>27:29</td>
<td>57:04</td>
</tr>
<tr>  <th scope="row">Todd</th>
<td>7:01</td>
<td>24:21</td>
<td>50:35</td>
</tr>
</tbody>
</table>

See Using id and headers attributes to associate data cells with header cells in data tables for a specific example connecting data cells to one ore more header cell within a data table.

Note that the top headers for Name, 1 mile, 5 km and 10 km are all marked up with th elements, as are the row headers for Mary, Betsy, Matt and Todd. Each of these header cell have also been given the scope attribute values of col or row depending on whether they are column or row header cells.

One more method to associating header cells with data cells uses the colgroup and rowgroup values of the scope attribute. This markup technique is use to indicate headers spanning multiple columns or rows. Consider the following table from Mozilla's Learn HTML Developer Docs:

Items Sold August 2016

		Clothes			Accessories
		Trousers	Skirts	Dresses	Bracelets	Rings
Belgium	Antwerp	56	22	43	72	23
	Gent	46	18	50	61	15
	Brussels	51	27	38	69	28
The Netherlands	Amsterdam	89	34	69	85	38
	Utrecht	80	12	43	36	19

Example including scope="colgroup" and scope="rowgroup" values on th elements

<table>
<caption>Items Sold August 2016</caption>
<tbody>
<tr>
<td></td>
<td></td>
<th colspan="3" scope="colgroup">Clothes</th>
<th colspan="2" scope="colgroup">Accessories</th>
</tr>
<tr>
<td></td>
<td></td>
<th scope="col">Trousers</th>
<th scope="col">Skirts</th>
<th scope="col">Dresses</th>
<th scope="col">Bracelets</th>
<th scope="col">Rings</th>
</tr>
<tr>
<th rowspan="3" scope="rowgroup">Belgium</th>
<th scope="row">Antwerp</th>
<td>56</td>
<td>22</td>
<td>43</td>
<td>72</td>
<td>23</td>
</tr>
<tr>
<th scope="row">Gent</th>
<td>46</td>
<td>18</td>
<td>50</td>
<td>61</td>
<td>15</td>
</tr>
<tr>
<th scope="row">Brussels</th>
<td>51</td>
<td>27</td>
<td>38</td>
<td>69</td>
<td>28</td>
</tr>
<tr>
<th rowspan="2" scope="rowgroup">The Netherlands</th>
<th scope="row">Amsterdam</th>
<td>89</td>
<td>34</td>
<td>69</td>
<td>85</td>
<td>38</td>
</tr>
<tr>
<th scope="row">Utrecht</th>
<td>80</td>
<td>12</td>
<td>43</td>
<td>36</td>
<td>19</td>
</tr>
</tbody>
</table>