Data tables should not be used to force content into visible columns. This was a frequently abused technique in the past, but multi-column layouts can now be attained using CSS to handle layout and positioning.

That said, data tables are still useful for presenting data in rows and columns. A few specific HTML tags are required in order to ensure that  data tables that are accessible to screen reader users. Without these tags, users who are unable to see the table can find it very difficult or impossible to understand the relationships between table headers and the cells within their scope.

The specific tags required depends on whether the table is simple or complex.

Simple Table

A simple table has a single header at the top of each column, and optionally a single header in the first column of each row. It has no nested columns or rows. To make a simple table accessible, apply the following techniques:

• Markup all column headers or row headers as table headers using the <th> element.
• Define the scope of each <th> using the scope attribute (the value of scope can be either “col” or “row”)

Complex Table

A complex table is any table that is not a simple table, as defined in the preceding section. There might be nested rows or columns, or headers might be located in places other than the first row or column. These sorts of tables can be very challenging for screen reader users to understand. To ensure their accessibility, apply the following techniques:

• Markup all column headers or row headers as table headers using the <th> element.
• Add a unique id attribute to each <th> element.
• For every table data cell (<td>), add a headers attribute that lists the id’s of all headers that apply to that particular cell. If more than one header applies to a cell, separate id’s with a space.