[basic.scope.class]

Any declaration of a class or class template C introduces a class scope that includes the member-specification of the class-specifier for C (if any).

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.

[Note 1:

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]

— end note]