In the DLang specification here: https://dlang.org/spec/struct.html#AnonUnionDeclaration

It is said that anonymous unions can be declared, but the ramifications of this are never clarified. Those coming from C++ will suspect that it makes the anonymous union members members of the containing object, but for those coming from Java or another language, this behaviour will seem unexplained.

Example below:
```
void main()
{
  import std.stdio;
  struct Bob {
    int a;
    union {  // Anonymous union.
      int b;
      int c;
    }
    union Cat {
      int d;
      int e;
    }
    Cat cat;
  }
	
  Bob bob = Bob(1, 2);
  assert(bob.a == 1);
  assert(bob.b == 2);
  assert(bob.c == 2);
  bob.cat = Bob.Cat(3);
  // assert(bob.d == 3); // ERROR, Bob has no property 'd'.
  assert(bob.cat.d == 3);  // OK
}
```