https://twitter.com/kumagi/status/1544911843164008449?s=20&t=59BqRDY6vul4E2c4HLw8sw

InnterclassAccess.cs

void Main()
{
    new Foo().Run(); // Foo.M
}

public class Foo
{
    public void Run() { new Bar().M2(); }
    private static void M() { Console.WriteLine("Foo.M"); }
    
    private class Bar
    {
        public void M2()
        {
            // Can access prarent class's private member.
            M();
        }
    }
}