The content below uses aria-live, aria-atomic and aria-relevant.
The time is now:
The clock has aria-live="off "- We do not want it to bother users just because the clock changed.
The normal alert has aria-live="polite" - We want to interrupt people at the next convenient point.
The rude alert is set to aria-live="assertive" - We want to interrupt people right now
The rude alerts will bug the user every x seconds...ongoing
However every time we bug them we only want to say the new alert text so...aria-atomic="false" (only read new content)
When we clear the rude alert, we do not want to hear all the alert messages that were deleted so aria-relevant="additions ". Note this is the default, so we did not really have to set it, but it shows the point.