Extending a struct which is inside another struct

Question

I'm trying to extend a struct that is already inside a struct. When I write the following code, I get

declaration is only valid at file scope.

struct A {
    struct AA {

    }
}

extension A {
    extension AA {

    }
}

Is it invalid to write an extension inside an extension?

Answer 1

It seems like the only way to do that is:

extension A.AA
{
   func test()
   {
      print("Test")
   }
}

It just worked in my playground