For each non-friend redeclaration or specialization
whose target scope is or is contained by the scope,
the portion after the
declarator-id,
class-head-name, or
enum-head-name is also included in the scope.
Lookup from a program point
before the class-specifier of a class
will find no bindings in the class scope.
[Example 1: template<class D>struct B {
D::type x; // #1};
struct A {using type =int; };
struct C : A, B<C>{}; // error at #1: C::type not found — end example]