Constrain to X and Y only

[Bryan Thatcher]

I'm trying to set up a user controlled game object where they follow the spline but have control to move either direction on the spline and in the Z direction. Basically just use the spline as a path they are constrained to but otherwise can control the gameobject. None of the examples I liked at jumped out as a good starting point.

Also, I'm a long time user and was disappointed to see it had been depreciated. I'm looking to checking out the update. Thanks.