Interchanging class & struct keyword in C++

Question

I was reading about one of the strange C++ feature called Injected class name here.

I tried following simple program

#include <iostream>
class test
{
    int s{3};
    public:
    int get_s()
    { return s; }
};
int main() {
    class test::test s;  // struct test::test s; also allowed. Why???
    std::cout<<s.get_s();
}

If I replace class keyword with struct in first line of main() program still compiles & runs fine. See live demo here. Why? Shouldn't I get compiler error? Why it compiles fine?

Answer 1

I believe the relevant verse is in 7.1.6.3/3 (highlighting mine, quoted here from a draft of the C++17 Standard):

Thus, in any elaborated-type-specifier, the enum keyword shall be used to refer to an enumeration (7.2), the union class-key shall be used to refer to a union (Clause 9), and either the class or struct class-key shall be used to refer to a class (Clause 9) declared using the class or struct class-key.

So either keyword can be used to stipulate the scope within which the injected class name exists, irrespective of which was used to declare/define test.