Unity3d lookat parameter description

Unity3d LookAt Parameter description  

//
        //  Abstract : 
        //     Rotates the transform so the forward vector points at target's current position.
        //
        //  Parameters : 
        //   target:
        //     Object to point towards.
        //
        //   worldUp:
        //     Vector specifying the upward direction.
        public void LookAt(Transform target, Vector3 worldUp);

among target Target for orientation ,worldUp Rotate the object itself after facing the target , bring worldUp vertical z Axis up ;

transform.LookAt(target,transform.right);	

transform.LookAt(target,-transform.right);	

transform.LookAt(target,transform.up);	

transform.LookAt(target,-transform.up);