How one can dynamic_cast from std::exception to std::nested_exception?

I've just seen a code containing dynamic_cast from std::exception to std::nested_exception, for instance,

try {
    std::throw_with_nested(std::runtime_error("error"));
} catch (std::exception &e) {
    auto &nested = dynamic_cast<std::nested_exception&>(e);
    std::cout << "ok" << std::endl;
}

At the very first time, I thought this code won't be compiled because std::nested_exception is not derived from std::exception and I expected dynamic_cast would do static check of inheritance but I was wrong.

Although I couldn't find related standard specification which explicitly mentions that dynamic_cast allows this, I confirmed that all three major compilers(clang/gcc/msvc) allow dynamic_cast between totally unrelated types.

But still, std::nested_exception is not derived from std::exception, so I thought the dynamic_cast will throw an bad_alloc exception and "ok" never printed. I was wrong again.

Now, I'm wondering how this can work. Is this a something special and exceptional for std::exception and std::nested_exception? Or, can I make another successful dynamic_cast<A&>(b) where type A and type of object b do not have common base class?