X3D mysterious field

http://www.web3d.org/x3d/specificati...ml#SliderJoint

| SliderJoint : X3DRigidJointNode {
| SFVec3f [in,out] axis 0 1 0
| SFNode [in,out] body1 NULL [RigidBody]
| SFNode [in,out] body2 NULL [RigidBody]
| MFString [in,out] forceOutput "NONE" ["ALL","NONE",...]
| SFFloat [in,out] maxSeparation 1 [0,)
| SFNode [in,out] metadata NULL [X3DMetadataObject]
| SFFloat [in,out] minSeparation 0 [0,)
| SFFloat [in,out] stopBounce 0 [0,1]
| SFFloat [in,out] stopErrorCorrection 1 [0,1]
| SFFloat [out] separation
| SFFloat [out] separationRate
| }
....
| The sliderForce field value is used to apply a force along the axis of the
| slider in equal and opposite directions to the two bodies.

???

Why is "sliderForce" missing in the declaration ?
An what is the purpose of such a field ? Forces are usually applied to
RigidBody nodes, not to Joints.

BTW: I would like to have a ODE like (dParam)fMax field instead 8-(

so long
MUFTI
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