How do I constrain location to a path I'm not sure if this is a "follow path" question, but I don't want this animated.

I have a parent handle empty that I want to be able to grab, and for that empty to only move along a nurbs path.

I can animate it but if I try to just grab the handle, it has no location limits.

Is this a simple setting I've missed?  Does the empty have to be parented to the path?
Not sure if this answers your question but if you add a follow path constraint to the empty, check fixed position and then move the offset from zero to one the empty is locked on to the curve which now functions as it's path. I really hope this helps and I didn't misunderstand the question.

(I then, just for effect, parrented the cylinder to the empty, to visualize a handle.)

Here's a picture of the setup.