When deleting recurring appointments, pop up should ask "Are you sure you want to delete this?"
When I have to delete a single occurrence in a recurring appointment, it would be good to have a pop up that confirms you want to delete. I have accidentally deleted a "series" and had to go back and try to add it back as it was. If a pop up had prompted me, I could say "No" and then delete just the occurrence.
Display a warning message when deleting an appointment from the calendar. Something like "Are you sure you want to delete?" or "Delete appointment?"