In the 3D space you can rotate objects around the X,Y and Z axis. You can either do this around the world axis, the way its done with vectorUp and VetorDir or the way I would prefer and seems more reasonable around the model axis. A shematic view of the angular velocity where the object is represented by the red ring. http://upload.wikimedia.org/wikipedia/commons/7/72/Gimbaleuler.svg
Links to the VBS wiki page:
http://resources.bisimulations.com/wiki/velocityAng
http://resources.bisimulations.com/wiki/setVelocityAng