[temp.explicit] p4

If the explicit instantiation is for a class or member class, the elaborated-type-specifier in the declaration shall include a simple-template-id; otherwise, the declaration shall be a simple-declaration whose init-declarator-list comprises a single init-declarator that does not have an initializer.

The intent is, in the explicit instantiation for a class or member class, the declaration of the explicit instantiation shall only be an elaborated-type-specifier. But, that expound does not reflect that meaning.

template<class T>
struct A{
    template<class Y>
    struct B{};
};
template 
template<> struct A<int>::B<int>; // error, the declaration is a explicit-specialization

Is the first sentence should be that

If the explicit instantiation is for a class or member class, the declaration shall be a simple-declaration that omits the init-declarator-list where the defining-type-specifier shall be an elaborated-type-specifier that includes a simple-template-id;

As the manner as the second sentence(emphasized part), which will restrict that the declaration couldn't be anything other than a special elaborated-type-specifier.