Are `signature_of` and in/out operators part of the intended API?

[JohannesSchilling]

[sorry if this is more of a support request than a regular issue, i guess you could phrase it as "please document" instead though]

I have tried to use custom structures as arguments/return value of D-Bus handler methods in my project, like this:

struct MyFoo {
  bool a;
  int b;
};

namespace sdbus {
  template <>
  struct signature_of<MyFoo> {
    static constexpr bool is_valid = true;
    static const std::string str() {
      return signature_of<sdbus::Struct<bool, int>>::str();
    }
  }
}

sdbus::Message& operator>>(sdbus::Message& msg, MyFoo& foo) {
  msg.enterStruct("bi");
  msg >> foo.a;
  msg >> foo.b;
  msg.exitStruct();
}

This makes me able to use MyFoo as parameter to D-Bus methods, but it's not documented anywhere and so i'm kind of wondering if that is intended API surface or more of an accidental internal detail that i'm using here..