1、qualified-id、nested-name-specifier：

[example:

struct  A {

    struct B {

        void F();

    };

};

• A is an unqualified-id.
• ::A is a qualified-id but has no nested-name-specifier.
• A::B is a qualified-id and A:: is a nested-name-specifier.
• ::A::B is a qualified-id and A:: is a nested-name-specifier.
• A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.
• ::A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.

end example]

qualified id

qualifier

specifier

base-class subobject

http://*.com/questions/3785789/what-is-the-meaning-of-qualifier