Create a new event for alerts, notifications, infobars, live regions, etc.
Orca currently listens for the "showing" event to present notifications and tooltips to the user. I've been told that the Gtk developers are hesitant to fire a showing event on such items (e.g. toasts) because they cannot know from the application side if the object is really showing. Fair enough. But I'm extremely hesitant to do what has been suggested, namely to present them when they are added to the accessibility tree: Just because something is added to the tree does not mean it's definitely something to present. I think we need a new event for this use case.
I mentioned live regions in the title because ARIA Live Regions have historically been a mess, with the official mapping to children-changed and text-changed events. Those mappings are problematic because we see those same events in response to DOM mutations and don't really know if it's a live region event or not. Having a dedicated event would solve this problem too.