The most common use of ARIA live is to announce a change in state to
the user as soon as possible without interrupting. Using
aria-live="polite", the message will be announced the
next time the user is idle.
Far less common but occasionally useful is to be able to announce an
important time-sensitive message by using
aria-live="assertive". Please note that user agents or
assistive technologies mY choose to clear queued changes when an
assertive change occurs. (e.g., changes in an assertive region may
remove all currently queued changes).
In addition to aria-live allowing us to set priority of
our messaging, there is also aria-relevant that lets us
define what types of changes should be presented. This example
simulates a chat app where messages are appended to a growing list,
in this case it would be appropriate for only additions to be
announced to the user with aria-relevant="additions".
Hey lookit that cool button down there, I wonder what that does?