What happens when you try to manual focus while the lens is auto-focusing?

I'm talking about the lenses that has all-time manual focus ability like higher-end Canon and Nikon lenses. When you half-press the shutter and the lens is hunting for focus, what happens when you try to rotate the ring in this process? Does the lens ignore your override or not?

Added (1). I'm just interested in lens optics but I haven't got one to try it myself or a friend that I can borrow one.

Why would you do such a thing

If you need to focus manually, set the lens to manual focus.

Most lenses will ignore what you are doing and continue to try and force the focus, ignoring this action may cause damage to the lens focusing mechanism or the camera. There are a very few, top end lenses, that will detect your action and so drop out of AF automatically, but they are the rare exception. A few cameras have variants on DMF (Direct Manual Focus) which will attempt to gain focus automatically, but once they are happy will drop the lens into AF mode.

*I'm a little short of a dozen lenses in my bags, one of these auto senses over-rides, all but three of the others will work with the cameras DMF mode(s).

You have to let the lens focus first and then, with shutter still half pressed, do the manual fine tuning.

You will not hurt the Canon USM lenses at all. The non USM lenses can be damaged if you force manual focus with the lens not in the manual focus switch position.

This is built into all of the newer Pentax lenses, you can half press the shutter for auto focus then 'tweak' focus by just rotating the focus ring which automatically dis-engages auto focus as long as you still keep the half shutter pressed, it's very quick and easy, and gets around the problem of auto focus not focusing where you want it to. If you release the shutter and half press it will auto focus again.