Test case: ARIA live regions

This is a (very rough) prototype to test the way ARIA live regions work with screen readers.

The script triggers three consecutive notifications. There is a 250ms delay between each notification. The live region is set to "polite", meaning that screen readers should speak each notification in its entirety before speaking the next.

The notifications are:

1. "This is the first notification. It is intended to take longer than one second for a screen reader to speak, so the concatenation of notifications can be tested."
2. "Ping!"
3. "This is the third notification."

Note: with apologies, the prototype is only working in Chrome at the moment.