Thanks. I Googled this for about three hours without any satisfaction.
Let me ask a related question. In the SysV init system, if some maintenance script saw that a service was down and wanted to know whether it ought to be restarted, it could check the current runlevel, and then look in the rc.d directory for that runlevel to see if the service had an "S" script or a "K" script. If it had an "S" script, it would mean that the service ought to be up in the present runlevel and should be restarted.
What is the parallel for systemd? Let's say that I am a maintenance script. I wake up and I see that bluetooth is down. How do I know whether or not it is supposed to be up? In the initd system, first I would have to check what runlevel I was running in. In some runlevels it should be up and in some it should be down. How does this work for systemd?