Another important technique in fine-tuning the experience for assistive technology users involves ensuring that only relevant parts of the page are exposed to assistive technology. There are several ways to ensure that a section of the DOM does not get exposed to accessibility APIs.
First, anything that is explicitly hidden from the DOM will also not be included in the accessibility tree. So anything that has a CSS style of
visibility: hidden or
display: none or uses the HTML5
hidden attribute will also be hidden from assistive technology users.
However, an element that is not visually rendered but not explicitly hidden is still included in the accessibility tree. One common technique is to include "screen reader only text" in an element that is absolute positioned offscreen.
Also, as we have seen, it's possible to provide screen reader only text via an
aria-describedby attribute referencing an element that is otherwise hidden.
See this WebAIM article on Techniques for hiding text for more information on creating "screen reader only" text.
Finally, ARIA provides a mechanism for excluding content from assistive technology that is not visually hidden, using the
aria-hidden attribute. Applying this attribute to an element effectively removes it and all of its descendants from the accessibility tree. The only exceptions are elements referred to by an
<div class="slide" aria-hidden="true">
<div class="slide" aria-hidden="true">
For example, you might use
aria-hidden if you're creating some modal UI that blocks access to the main page. In this case, a sighted user might see some kind of semi-transparent overlay indicating that most of the page can't currently be used, but a screen reader user may still be able to explore to the other parts of the page. In this case, as well as creating the keyboard trap explained earlier, you need to make sure that the parts of the page that are currently out of scope are
aria-hidden as well.
Now that you understand the basics of ARIA, how it plays with native HTML semantics, and how it can be used to perform fairly major surgery on the accessibility tree as well as changing the semantics of a single element, let's look at how we can use it to convey time-sensitive information.
aria-live lets developers mark a part of the page as "live" in the sense that updates should be communicated to users immediately regardless of the page position, rather than if they just happen to explore that part of the page. When an element has an
aria-live attribute, the part of the page containing it and its descendants is called a live region.
For example, a live region might be a status message that appears as a result of a user action. If the message is important enough to grab a sighted user's attention, it is important enough to direct an assistive technology user's attention to it by setting its
aria-live attribute. Compare this plain
<div class="status">Your message has been sent.</div>
with its "live" counterpart.
<div class="status" aria-live="polite">Your message has been sent.</div>
aria-live has three allowable values:
aria-live="polite"tells assistive technology to alert the user to this change when it has finished whatever it is currently doing. It's great to use if something is important but not urgent, and accounts for the majority of
aria-live="assertive"tells assistive technology to interrupt whatever it's doing and alert the user to this change immediately. This is only for important and urgent updates, such as a status message like "There has been a server error and your changes are not saved; please refresh the page", or updates to an input field as a direct result of a user action, such as buttons on a stepper widget.
aria-live="off"tells assistive technology to temporarily suspend
There are some tricks to making sure your live regions work correctly.
aria-live region should probably be set in the initial page load. This is not a hard-and-fast rule, but if you're having difficulty with an
aria-live region, this might be the issue.
Second, different screen readers react differently to different types of changes. For example, it's possible to trigger an alert on some screen readers by toggling a descendant element's
hidden style from true to false.
Other attributes that work with
aria-live help you fine-tune what is communicated to the user when the live region changes.
aria-atomic indicates whether the entire region should be considered as a whole when communicating updates. For example, if a date widget consisting of a day, month, and year has
aria-atomic=true, and the user uses a stepper control to change the value of just the month, the full contents of the date widget would be read out again.
aria-atomic's value may be
false (the default).
aria-relevant indicates what types of changes should be presented to the user. There are some options that may be used separately or as a token list.
- additions, meaning that any element being added to the live region is significant. For example, appending a span to an existing log of status messages would mean that the span would be announced to the user (assuming that
- text, meaning that text content being added to any descendant node is relevant. For example, modifying a custom text field's
textContentproperty would read the modified text to the user.
- removals, meaning that the removal of any text or descendant nodes should be conveyed to the user.
- all, meaning that all changes are relevant. However, the default value for
additions text, meaning that if you don't specify
aria-relevantit will update the user for any addition to the element, which is what you are most likely to want.
aria-busy lets you notify assistive technology that it should temporarily ignore changes to an element, such as when things are loading. Once everything is in place,
aria-busy should be set to false to normalize the reader's operation.