RHO opens 1♣, you double and partner responds 1NT which is passed back to you. What does a bid of 2♦ show?  Is it weak, trying to improve the partscore, e.g. K9xx  AJx  KQ109x  x, or does it show extras?

I think a bid of 2M would be forcing, but am not sure about 2♦. 

Seems like I remember from somewhere that if you double a major and then bid a lower-ranking suit at the 2 level over partner's 1NT that would be NF, maybe   x   Q9xxx  AKx  KJxx  if you doubled a 1♠ opening. 

The actual hand that initiated this discussion over a couple of drinks after the afternoon local duplicate was A10xx  AQxx  KQ9xx  void.   You double 1♣, and pard responds 1NT.  What is your action?