How to inteprete the output of getConstraintState?

[ChengshuLi]

For a fixed constraint, getConstraintState returns a vector of length 6. The documentation says they are the applied constraint forces.

Are these the magnitudes of 6 different forces? If so, what are the directions of these forces?
Or are these two forces in 3D space (6-d in total)?
Lastly, is the unit of these values Newton?

Thanks a lot!

[erwincoumans]

The fixed constraint fixes 6 degrees of freedom, so the size is 6: 3 linear and 3 angular components.