I've never seen them interrupt a show in progress. I've seen them do pledge drives where they preempt a show, but I haven't ever had something I was watching on

I've never seen them interrupt a show in progress. I've seen them do pledge drives where they preempt a show, but I haven't ever had something I was watching on PBS be interrupted, personally. Maybe I'm just lucky, or maybe they do it differently in the places I've lived?