Is Override Still Mandatory?

[Vijay Nayar]

I was under the impression that the attribute "override" was 
mandatory when replacing a virtual function in a base class.  
However, code that leaves this out has no errors using dmd v2.060.

import std.stdio;

class A {
   this() {
     show();
   }
   void show() {
     writeln("A");
   }
}

class B : A {
   this() {
     super();
   }

   // No override and no compiler errors?
   void show() {
     writeln("B");
   }
}

void main() {
   auto b = new B();
   // This prints "B".
}

Also, is there a way to make class A call it's own version of 
show()?

  - Vijay