Tailsitter sdf, why elevator and rudder?

I’m looking at the tailsitter example for SITL Gazebo. Why are there entries (link/joint/control channel) for an elevator and rudder? I thought the tailsitter would only have elevons.

If I comment out the elevator and rudder entries, it sure doesn’t fly stably in FW mode.

There are no visuals for the elevator or rudder, although there isn’t a visual for the elevons either. I actually tried adding a mesh for the elevons, and they appear to move appropriately.

Update: after further investigation. The “rudder” isn’t actually driven by a control channel, so it doesn’t really move. It must be conceptually, just a fin. Perhaps it represents the combined aerodynamic action of those two inverted-V fins that it stands on when it’s on the ground.