Quiet Commute Day, "Interline" buses

As I've been riding the bus, I've noticed more and more buses showing "Interline" on their route-signs, and wondered what that meant, exactly. So I asked. In retrospect, it should've been obvious, so I'll blame lateness of the hour and/or lack of coffee for me not making the connection and being able to answer it for myself.

Each route is a "line," in RTD parlance. From time to time, a bus may need to be taken out of service for one line, and put back into service for another (if a bus breaks down, or presumably gets swamped - I didn't think to ask under what circumstances that can/does happen). When they do that, they switch their route-signs to "Interline" so that people who might be expecting to see that route (before or after the switch) won't feel as though they are being skipped at a stop. Pretty straightforward, actually. I even saw an "Interline" bus change to a normal route the day I asked the question, as I was leaving the Park-n-Ride.