It's in the car physics demo script. If one has the latest version installed: 6.31.3 then it is compatable. In other words you can run the demo script with no changes. I thought I was going mad when I first tried to run the script as I had found functions that expected nullvector accepting 0 and also found that new phent_angvelocity function. SED doesn't recognize it and it's not documented yet to my knowledge but it must exist as it's compiling. To be more specific it's located within the physics_car.wdl script.