[mycroft]

I hate asking "feed me" questions, but I've tried to look, and am finding nothing (which probably means my search string isn't quite right). Very happy with "go here" answers!

I'm being convinced by both the people suggesting that doubles after 1NT-(something) should be negative, rather than penalty, and the hands that have cried out for a negative double, and want to switch. However, I can't find anything on the "other stuff". Things like:

- does a X create a force, and if so through where? What kind of strength is responder promising?
- when does opener protect after responder passes? If partner pulls the protective double, what kind of hand do we expect?
- responder's second-round actions? What if responder's hand is 3-in-a-major, and opener picked that major?

Any breadcrumbs would be appreciated; information based on a 12-14 NT (or "things to think about being different with a 12-14") doubly so - especially as the biggest results we get from a weak NT have been when they step into the grinder.

[antonylee]

I play that X does NOT create a force (if I want to force, I start with Stayman (Rubensohl, in my methods)) so it's competitive/light invite, or sometimes stronger but with an awkward shape for your other bids. Opener always protect with up to Qx in overcaller's suit, and pulling just means "I want to play there" (if the suit could not have been bid naturally earlier) or suggests two places to play (if the suit could have been bid earlier, e.g. 1N (2♥) P (P) X (P) 2♠: I could have bid 2♠ immediately).
If responder is say 3244 and the auction goes 1N (2♥) X (P) 2♠ I would start with 3♥ and see where it goes...

[Codo]

1. X is not forcing. First of all you can sit. And second: You can usually jump to invite, or cuebid to force. You may use 2 NT as a non natural bid although.
2.With any doubleton that is weak enough. I would not protect over 1 NT (2♥) pass (pass) with Kxx,AK,Kxxx,xxxx, but else, I would.
3. If resonder doubled with just three card in a major, he has two alternatives: Let partner play the 4-3 fit- not a bad thing with the short trumps ruffing opponents long suit- or have another string in the bow, like NT etc. But do not fear 4-3 fits. They are usually nice to play. Not always nice in the sense of easy, but nice in the sense of makeable with good declarer play...

[Zelandakh]

One sensible approach is to play that double promises enough strength to be happy if Opener passes. The weaker you allow Responder to double the less able Opener is to pass, so you have to balance fighting for the part score against this. You also have to decide whether double then bid shows an invitational hand or just the other 2 suits. One interesting alternative is for double to show specifically a doubleton in their suit most of the time, perhaps occasionally 3.

On your specific questions:-
1a. You are not creating any force.
1b. Double promises whatever strength you agree to. Lower requirements are better for fighting the part score, stronger requirements are easier for Opener to deal with. I suggest starting with a conservative approach where double shows some values and then devaluing if you find you are getting robbed too often.
2a. Opener will usually double back in with a doubleton unless very defensive and can also back in by bidding a 5 card suit at the 2 level.
2b. Any hand that does not want to sit for a penalty.
3a. You have 2 choices for double then bid as described above. How you play these sequences might depend on the rest of your structure. For example, if you have no invite with hearts available then playing 1NT - (2♠) - X - (P); 3m - (P) - 3♥ as covering this hand type makes sense. Less clear is 1NT - (2♠) - X - (P); 3♣ - (P) - 3♦ which is useful both as an invite and as "pick a red suit". Best to define some rules that work for you and stick to them. For example: "doubling then bidding the suit below theirs is an invite; doubling and bidding any other suit is scramble."
3b. No need to be scared of a 4-3 fit here. Partner might even have 5. If you do not like these kinds of bread-and-butter part-score hands then the weak NT is probably not the right choice in the first place.