Web is no more static. Interactive content with contributing to the web while retrieving the information on one side and instant, dynamic and specific information retrieval on the other side, the modern web is more dynamic. The websites that show the stock updates, live games make the web content even more dynamic and instantaneous. Introduction of live chat features on many websites made the life of users more comfortable.
In all the situations above the common thing is that a portion of the web page updates frequently. The frequency depends on various factors. The user notification of dynamic updates is critical here. The judgement of how the user should be notified must be well thought. It is not apparent that every update need to be informed immediately unless the user is interacting with a service agent via live chat.
The updates that are displayed on the page frequently may even interrupt the current activity of the user if he don’t wish to receive immediate updates. To handle these dynamic updates more efficiently W3C WAI ARIA introduced aria-live property.
How frequently do you need the updates ?
Assertive : The user need to be notified about the update immediately i.e. as soon as the content is displayed on the screen. Using aria-live=“assertive” interrupts what the user currently is doing to notify the update. Appropriate for a live chat.
Polite: Using aria-live=“polite” allows the user to do whatever they are currently doing. May be reading a paragraph with the screen reader. Once the user completes the current task then the message is notified to the user.
Off: Some user does not want to notify the updates at all or that might not be relevant for them. Using aria-live=“off” completely switches off the updates.
Detailed information on handling dynamic content is discussed in advanced accessibility training course.