The techniques for dealing with data tables that we discussed so far are designed to give an overview of the table. These are not required by the Section 508 Standards. The next two techniques deal with the internals of the table. These techniques will enable you to satisfy the following two Section 508 Standards:
Row and column headers shall be identified for data tables.
Markup shall be used to associate data cells and header cells for data tables that have two or more logical levels of row or column headers.
Let's look first at 1194.22(g) that requires that you, in effect, label table headers as html headers (th), not unlike what we talked about in the Navigation lesson where heading text should be marked up as HTML headings (h1, h2, etc).
Each table cell is either a pure data cell (td) or a header cell (th). By default, headers will appear centered in bold so that most users can easily identify them. If this is not exactly the way you want your headers to appear, you can modify their appearance using style sheets. By labeling a cell as a th, you are identifying it as a table header as required by Â§1194.22 (g).
In addition to making the headers stand out, they can be identified by assistive technology so that when a talking browser is reading a specific cell it can, on command, search for the header cells and announce them. In addition, as the user moves from cell to cell, the assistive technology will announce the row and column headers that have changed. For example, moving across the Business class row in the Oceana Airlines Dinner Service table above, a screen reader user would hear, "Appetizer, Shrimp Cocktail, Salad, Mixed Greens, Wine, Oceana Label Cardonnay or Merlot, Entree, Chicken Satay or Beef Tips, Desert New York Style Cheesecake."
Both the Lunch Menu table and the Oceana Dinner Service table above have headers specified as they should be. You can see those headers (th) in the HTML code for the Lunch Menu Table. You can also use the Web Accessibility Toolbar, Tables > Table headers; this will put a black background on all cells which are table header cells (th).
The Oceana Dinner Service table is a little different because of the ambiguity of whether the top left cell is a header for its column or its row. This is resolved using the scope attribute on that th cell, or, as is recommended by many, on every th cell. The possibilities are scope="col" (which is appropriate for that top left cell) or scope="row". Here is the code for the first two rows of the Dinner Service table.
<tr> <th scope="col">Class of Service</th> <th>Appetizer</th> <th>Salad</th> <th>Wine</th> <th>Entree</th> <th>Dessert</th> </tr> <tr> <th>Economy</th> <td>Peanuts</td> <td>None</td> <td>Complimentary Soft Drinks, Liquor for Purchase</td> <td>Ham and Cheese Sandwich</td> <td>Packaged Cookies</td> </tr>
The coding for this table has evolved since it first appeared in Mike Paciello's book (Paciello, Michael G., Web Accessibility for People with Disabilities, Lawrence, Kansas: CMP Books, 2000); Mike used headers/id markup (more about that later) which is not necessary. The earlier version of this course included the scope attribute on all cells, not just the one cell whose scope is ambiguous. When you are using th cells, assistive technology knows they are headers and can deduce the scope; so the extra scope attributes are not necessary.
With the table marked up this way, a screen reader would announce the cells in the second row something like this: "Appetizer, Peanuts; Salad, None;" etc.
Alternative to using header cells (th) with the scope to resolve ambiguity, you can use data cells (td) with the scope attribute on any cell that is a heading. This technique has the advantage that you don't have to go back and restyle the heading text. Any cell is a heading if it is a th or it is a td with a scope attribute.