Success Criterion 2.4.3: Focus Order

Understanding Success Criterion: 

If a Web page can be navigated sequentially and the navigation sequences affect meaning or operation, focusable components receive focus in an order that preserves meaning and operability.

Accessibility Level: 
A
Intent of Success Criterion: 

The intent of this Success Criterion is to ensure that when users navigate sequentially through content, they encounter information in an order that is consistent with the meaning of the content and can be operated from the keyboard. This reduces confusion by letting users form a consistent mental model of the content. There may be different orders that reflect logical relationships in the content. For example, moving through components in a table one row at a time or one column at a time both reflect the logical relationships in the content. Either order may satisfy this Success Criterion.
The way that sequential navigation order is determined in Web content is defined by the technology of the content. For example, simple HTML defines sequential navigation via the notion of tabbing order. Dynamic HTML may modify the navigation sequence using scripting along with the addition of a tabindex attribute to allow focus to additional elements. If no scripting or tabindex attributes are used, the navigation order is the order that components appear in the content stream. (See HTML 4.01 Specification, section 17.11, "Giving focus to an element").
An example of keyboard navigation that is not the sequential navigation addressed by this Success Criterion is using arrow key navigation to traverse a tree component. The user can use the up and down arrow keys to move from tree node to tree node. Pressing the right arrow key may expand a node, then using the down arrow key, will move into the newly expanded nodes. This navigation sequence follows the expected sequence for a tree control - as additional items get expanded or collapsed, they are added or removed from the navigation sequence.
The focus order may not be identical to the programmatically determined reading order (see Success Criterion 1.3.2) as long as the user can still understand and operate the Web page. Since there may be several possible logical reading orders for the content, the focus order may match any of them. However, when the order of a particular presentation differs from the programmatically determined reading order, users of one of these presentations may find it difficult to understand or operate the Web page. Authors should carefully consider all these users as they design their Web pages.
For example, a screen reader user interacts with the programmatically determined reading order, while a sighted keyboard user interacts with the visual presentation of the Web page. Care should be taken so that the focus order makes sense to both of these sets of users and does not appear to either of them to jump around randomly.
For clarity:

  1. Focusable components need to receive focus in an order that preserves meaning and operability only when navigation sequences affect meaning and operability.
  2. In those cases where it is required, there may be more than one order that will preserve meaning and operability.
  3. If there is more than one order that preserves meaning and operability, only one of them needs to be provided.
Specific Benefits of Success Criterion: 

These techniques benefit keyboard users who navigate documents sequentially and expect the focus order to be consistent with the sequential reading order.

  • People with mobility impairments who must rely on keyboard access for operating a page benefit from a logical, usable focus order.
  • People with disabilities that make reading difficult can become disoriented when tabbing takes focus someplace unexpected. They benefit from a logical focus order.
  • People with visual impairments can become disoriented when tabbing takes focus someplace unexpected or when they cannot easily find the content surrounding an interactive element.
  • Only a small portion of the page may be visible to an individual using a screen magnifier at a high level of magnification. Such a user may interpret a field in the wrong context if the focus order is not logical.