ConfigurableJoint: Swing and Twist?

What the heck is Swing and Twist?

I am trying to set up a configurable joint to both translate in Y, and set it's angular velocity around Y.

From the documentation:

"angularYZDrive Definition of how the joint's rotation will behave around its local Y and Z axes. Only used if Rotation Drive Mode is Swing & Twist."

Yet, if I look up the documentation for Rotation Drive Mode, I get:

"Control the object's rotation with either X & YZ or Slerp Drive by itself."

There is no "Swing & Twist" option, only X&YZ and Slerp. Is Swing&Twist a pseudonym for one of these?

Also, changing the option does not help: I see no angular velocity changes after setting Target Angular Velocity.