What's the difference between void and cv void?

Question

I have come across the type "cv void" in the latest draft of the C++ standard (N4606) :

8.3.3 [dcl.mptr], paragraph 3

A pointer to member shall not point to a static member of a class (9.2.3), a member with reference type, or “cv void”.

With a little bit of research, I found "cv void" is a real type, but I have no idea what's the difference compared to the type void. Can you explain it with an example (maybe with a code) ?

---

EDIT :

• I sort of expected cv would stand for cv-qualified. My question here is, why do we need to "cv-qualify" the type void?
• The reason I said "cv void is a real type" is that, the standard actually defined it:

  3.9.1 [basic.fundamental], paragraph 9

  A type cv void is an incomplete type that cannot be completed; such a type has an empty set of values...

Answer 1

"cv void" is not a real type. "cv" here is a shorthand for "possibly cv-qualified", which means "may have a const or a volatile on it".

The passage means that a pointer-to-member may not point to an object of the following types: void, const void, volatile void and const volatile void. It's fairly obvious, since such objects cannot exist in the first place, but I guess it's nice to be clear.