[temp.expl.spec] p6

Members of an explicitly specialized class template are defined in the same manner as members of normal classes, and not using the template<> syntax. The same is true when defining a member of an explicitly specialized member class. However, template<> is used in defining a member of an explicitly specialized member class template that is specialized as a class template.

The rule seems not only applied to define that member but also includes explicit-specialization.

template<class T>
struct A{
    template<class Y>
    struct B{};
};

template<>
struct A<int>{
    template<class Y>
    struct B;
};

template<>
struct A<int>::B<int>{};

[class.mem.general] p6

A redeclaration of a class member outside its class definition shall be a definition, an explicit specialization, or an explicit instantiation ([temp.expl.spec], [temp.explicit]). The member shall not be a non-static data member.

Could we change the wording "define" to "redeclare" to include these cases?