New Minor Forcing (NMF) ♠ ♥ ♦  ♣ 
The NMF convention is a important tool to search the Opener's hand, like Check Back convention, after the follow sequence:
  Opener    Responder
 1 minor     1 major
    1nt        the other minor <= artificial bid to search the hand (NMF)

We can consider this convention integrated in 2/1 system.
In general the use of NMF by Responder is the start of a
possibly  Game Force (GF) auction.

To use NMF Responder need at least an invitation hand
(10-11 hcp), otherwise Responder should:
a) pass in 1nt:
b) sign-off auction rebidding his suit at level 2
    (Opener with 3 cards support should not support Responder);
c) make an invitation in his 6 cards major jumping to level 3
     (this means 10-11 hcp and asking for 3 cards or honor second);
d) bids sign-off in partner's minor with a simple raise;
e) make a invitation in partner's minor jumping to level 3; 
f) jumping to game (3nt / 4major / 5 minor / 4nt ...)

Rule#1 NMF establish some priorities in Opener's third bid:
Opener Response
1 minor 1 major
  1nt       NMF asking for explain Opener's hand
   ?
  1- Opener bids at level 2 first his 4 cards major suit;
  2- Opener support Responder's major with 3 cards;
  3- Opener bids 2nt if have stopper in unbid suits;
  4- Opener bids other minor suit to show 4-4 in minors;
  5- Opener rebid his suit if not satisfies these priorities.

Note1: NMF is off after any opponent interference
Opener Opponent Responder Opponent explanation
  1
♦        pass        1♠               pass       (1) penalty double
 1nt       x(1)         2
♣ <= 5♣+ cards sign-off - this is not NMF

Note2: NMF is off for passed hand (unless agreement was made)
Responder Opener
   pass        1
♦
    1
♠         1nt
    2
♣ <= 5♣+ cards sign-off (with 5♠4♣ rebid Spades or pass)
       
Note3: NMF here is not standard because here we prioritize the
information of a top honor in Responder's major.
Opener Responder
  1
♦       1♥
 1nt       2
♣  <= NMF
   ?
 2
♥ <= 3♥ cards support but no top honor (Responder can pass)
 2
♠ <= 3♥ cards support with a top honor (Hxx)
Note: 2
♠ in standard NMF denies stopper in ♠ and denies support.
2nt <= denies support in 
♥ but shows Spades stopper
 3
♣ <= denies support in ♥ and stopper in ♠ - shows 4♣ cards
 3
♦ <= denies support in ♥ and stopper in ♠ - shows 5♦ cards

Note4: Responder having no Hxx (jxxxx or worst) in his major, should avoid bid game in this suit, even with 13 hcp, because if Opener denies support with top honor he will lose 3 tricks in trump.
  
Let's Analyze in More Detail Some Sequences

Opener Responder 
 1
♣        1♥
 1nt       2
♦  => NMF
 ? 
=> 2
♥  minimum, support 3♥ cards without Hxx (A/K/Q)
=> 2
♠  minimum (12-13- hcp), support 3♥ cards with Hxx
=>2nt 12–14 hcp, no 
♥ support, ♠ stopper (A/K/QJx)
=> 3
♣  12-14 hcp 5♣ cards, no support ♥ no ♠ stopper
=> 3
♦  12-14 hcp 4♣-4, no ♥ support no Spades stopper
=> 3
♥  maximum (13+–14 hcp), 3♥ with Hxx, no control in ♠ 
=> 3
♠  maximum with ♥Hxx and control for Spades (A or K) 
=>3nt 15 hcp and 5431 singleton 
♥, with 1,5 stopper in ♠.
                             What is 1,5 stopper? = AJ9, KQx, KJ10

Opener Responder
  1
♣         1♠
 1NT        2
♦ => NMF
  ? 
=> 2
♥ minimum (12-13-hcp) with 4♥ cards, may have support in ♠
=> 2
♠ minimum (12-13-hcp), support 3 any cards in ♠, no 4♥ cards
=>2nt 12–14 hcp - no support 
♠, ♥ stopper (A/K/QJx)
=> 3
♣ 12-14 hcp - 5♣ cards, no support for ♠ no stopper ♥
=> 3
♦ 12-14 hcp - 4-4 minors, no support ♠ no stopper ♥ 
=> 3
♥ maximum 4♥ cards - support for ♠ with top honor (A/K/Q) 
=> 3
♠ maximum (13+–14 hcp), 3♠ cards with a top honor   
=>3nt 14-15 hcp - possible 5431 
♠ singleton, with 1,5 stopper ♥

Opener Responder 
 1
♦        1♥
1ST       2
♣  => NMF
 ? 
=> 2
♦ minimum (12-13- hcp), no support in ♥ and no stopper in ♠
=> 2
♥ minimum (12-13- hcp), 3♥ cards without Hxx 
=> 2
♠ minimum (12-13- hcp) with 3♥ cards with a top honor in ♥  
=>2nt 12–14 hcp, no support in 
♥, but with stopper in ♠
=> 3
♣ 12-14 hcp - 4-4 in minors, no support for ♥ no stopper in ♠
=> 3
♦ 12-14 hcp - 5♦ cards, no support in ♥ and no stopper in ♠
=> 3
♥ maximum (13+–14 hcp), support ♥ Hxx - no ♠ control
=> 3
♠ maximum (13+–14 hcp), support ♥ with control for ♠ (A or K)
=>3nt 14-15 hcp and possible 5431 
♥ singleton, with 1,5 stopper ♠

Opener Responder 
  1
♦        1♠
  1nt       2
♣  => NMF
  ? 
=> 2
♦  minimum (12-13- hcp), no support in ♠ and no stopper in ♥
=> 2
♥  minimum with 4♥ cards and can have support for ♠
=> 2
♠  minimum any 3 cards in ♠
=>2nt 12–14 hcp, no support for 
♠, with stopper in ♥
=> 3
♣  12-14 hcp - 4-4 in minors, no support for ♠, no stopper in ♥
=> 3
♦  12-14 hcp - 5♦ cards, no support for ♠ and no stopper in ♥  
=> 3
♥  maximum  with 4♥ cards and support to ♠ with Hxx 
=> 3
♠  maximum (13+–14 hcp) and support to ♠ with Hxx
=>3nt 14-15 hcp and possible 5431 
♠ singleton, with 1,5 stopper ♥   


 

SPECIAL SIGN-OFF IN 3♦ Opener Responder
  1
♣         1major
 1NT         3
 <= ♠Q9xx ♥xx 
♦KJ10xx ♣x  or ♠9x ♥J10xx ♦AK10xxx ♣x
 pass
Note5: Playing Walsh after 1
♣ we bid first the major and so after 1NT
we only can bid Diamonds sign-off at level 3 because 2
♦ is NMF. 

What is a Game Force (GF) and What is an Invitation to Game

INVITATION TO GAME
Opener:      
♠Axx ♥A10xx 
♦KJ9x ♣Jx
Responder: 
♠QJxx ♥Jxx 
♦AQxxx ♣x
Opener Responder 
  1
♦         1♠
  1nt        3
* => invitation showing 10-11 hcp
 pass
* Responder shows 10-11 hcp with support 4
♦+ cards.
Opener with minimum need pass.
So here Responder don't use NMF because there are
only 4
♠ cards and no strength to GF - just for invitation

--------------------------------------------------------------
GAME FORCE
O: 
♠xx ♥AQxx 
♦K9xxx ♣Ax
R: 
♠KQ9x ♥Kxx 
♦AQxx ♣x
Opener Responder 
  1
       1♠
  1nt       2
♣*  <= NMF
  2
♥         3
♦    <= GF
  4
♣**    4nt (RKB1430)
  5
♦         6♦
 pass
* before support Opener in 
♦ suit Responder
 need bid NMF to create a GF continuation
** if Opener has 
♣KJx he should bid 3nt, so
     here 4
♣ shows A♣.
----------------------------------------------------------------

INVITATION TO GAME
O: 
♠xx ♥Ax 
♦KJ10x ♣KJ108x
R: 
♠AQ7xx ♥ KJ6xx 
♦xx ♣x
Opener Responder 
  1
♣       1♠
  1nt      3
♥* => invitation
 pass
* Responder shows 10-11 hcp with 5-5 in the majors.
Opener 3
♠ is sign-off.
Opener should not bid 3nt just prefer the major or pass or big game in a major

----------------------------------------------------------------

GAME FORCE (GF)
O: 
♠xx ♥A1x 
♦KJ10x ♣KJ108x
R: 
♠AQJxx ♥KJ10xx 
♦Qx ♣x
Opener Responder
  1
♣       1♠
  1nt      2
♦ => NMF
  2nt      3
♥ => GF showing 5♠-5♥
  4
♥      pass
Opener in NMF denies 4
♥ cards so Responder's
3
♥ shows 5-5 and it is GF (12+ hcp)

-----------------------------------------------------------------

Examples Using NMF

O: ♠Qxx ♥AJx ♦QJx ♣KJ9x
R: 
♠Ax ♥K109xx 
♦Kxx ♣Qxx
Opener Responder
  1
♣         1♥
  1nt        2
♦ => NMF
  3
♥*       4♥
 pass
 * maximum with a top honor in 
♥

------------------------------------------------------

O: ♠Qxx ♥J7x ♦KJx ♣AJ9x
R: 
♠Kx ♥Q8xxx 
♦Axx ♣Qxx
Opener Responder
  1
♣        1♥
  1nt       2
♦  => NMF
  2
♥*     pass
* minimum, no top honor in 
♥ so
 with a suit Q8xxx no good chance to make 4
♥.
-----------------------------------------------------------

O: ♠Qxx ♥AJxx ♦Qx ♣KJ9x
R: 
♠K109xx ♥Kx 
♦x ♣AQxxx
Opener Responder
  1
♣         1
  1nt        2
♦  => NMF
  2
♥         3♣  => GF with 4♣+
  3
♠*       4♠
 pass
*Open first priority is bid his major 4
♥ cards then
  second priority is support 3
♠ cards with minimum.
With maximum Opener bid 3
♥ after
Responder's NMF showing both.

----------------------------------------------------------

O: ♠Qx ♥AJxx ♦Qxx ♣KJ9x
R: 
♠K109x ♥Kxx 
♦x ♣AQxxx
Opener Responder
  1
♣       1♠
  1nt       2
♦ => NMF (need for FG)
  2
♥        3♣  => GF with 4♣+ 
  4
♣*      5♣
* Opener has a weak hand to bid 5
♣
so make a game invitation -
Responder with singleton 
♦ accepts.

----------------------------------------------------

O: ♠Kx ♥xx ♦AQJxx ♣Kx
R: 
♠Ax ♥KJ109x 
♦10xx ♣AQx
Opener Responder 
  1
♦          1♥
  1nt         2
♣ => NMF
  2nt*       3nt
* minimum with stopper in 
♠ and no support
 in 
♥ so 3nt is a good contract to game.  
------------------------------------------------------------

O: ♠xx ♥Ax ♦AQxxx ♣K10x
R: 
♠x ♥KJ109x 
♦K10xx ♣AJx
Opener Responder 
  1
♦         1♥
  1nt*      2
♣  => NMF
  3
♦         5♦
*After denies stop in 
♠ and 3 cards support
  in 
♥ showing 5
♦ cards Responder jump to game
------------------------------------------------------------

O: 
♠Axx ♥AQxx 
♦KJ9x ♣xx
R: 
♠KQ9xx ♥KJxx 
♦AQx ♣x
Opener Responder 
  1
♦        1♠
  1nt       2
♣ => NMF
  3
♥*      4nt => RKB for ♥
  5
♠         6♥
 pass
* The information of maximum with honor in 
♠
is good for Slam after RKB showing trump's Queen.

-------------------------------------------------------------

O: 
♠10xx ♥AJx 
♦AQ9xx ♣Jx
R: 
♠J98xx ♥Qx 
♦xx ♣AKQ
Opener Responder 
  1
♦         1♠
  1nt        2
♣  => NMF
  2
♠         3♠*
 pass           
*support in 
♠ not define honor, so 3♠ is an invitation
asking for honors in 
♠ and with no honor Opener pass.

---------------------------------------------------------------

O: 
♠x ♥AJ10 
♦A109x ♣KQJ10x
R: 
♠KQ9xx ♥Kx 
♦Qxx ♣Axx
Opener Responder 
  1
♣         1♠
  1nt        2
♣  => NMF
  3nt*      pass
*singleton spades weakness  Responder's hand
  possible 5431, so Responder should pass.

--------------------------------------------------------------

O: 
♠x ♥AJ9 
♦A109x ♣KQJxx
R: 
♠A9xxx ♥Kx 
♦Kx ♣A1098
Opener Responder 
  1
♣       1♠
  1nt      2
♣ => NMF
  3nt      4
♣ => support in Clubs
  4
♦*    4nt => RKB1430 
  5
♦**  7♣ Opener has 5♣ cards 
* cue bid ** 3 key cards - crisscross play

--------------------------------------------------------------


You can use NMF also in level 3 after Opener jump to 2nt
NMF is used by Responder at level 3 asking for support in his 5th major
cards bid at level 1, or when have also 5
♠-4♥ or 4♥-4♠, but not when
Responder have 5-5 in the major or a 6 cards in a major.

Opener Responder
  1
♣         1♥
  2nt        3
♦  => NMF
    ?    After 3
 NMF Opener bids:
  3
♥ showing support in ♥ with 3 cards and can also have 4♠ cards,
             that will be bided if Responder bids 3nt that shows 4
♥-4♠;
  3
♠ showing 4♠ cards and denying 3♥ cards support;
  3nt to play - no 3 cards in 
♥ and no 4♠ cards;
  4
♣ cuebid - 4♥ cards and A♣ must have 1º or 2º control in ♠;
  4
♦ cuebid - 4♥ cards and A♦ must have 1º or 2º control in ♠ no A♣;
  4
♥ support of 4♥ cards and denies 1º or 2º control in ♠;    

-------------------------------------------------------------------------                

Opener Responder
  1
♣         1♠
  2nt        3
♦  => NMF
    ?     After 3
 NMF Opener bids:
  3
♥ showing 4♥ cards and can have 3 cards ♠ that will be bided
             if Responder bids 3nt showing only 5
♠ cards;
  3
♠ support with 3♠ cards and denying 4♥ cards;
  4
♠ support with 4♠ and denying 1º and 2º control in ♥;  
  3nt to play, no support for 
♠ and no 4♥ cards;
  4
♣ cuebid - 4♠ cards and A♣ with 1º or 2º control in ♥;
  4
♦ cuebid - 4♠ cards and A with 1º or 2º control in ♥ - no A♣;
  4
♥ cuebid - 4♠ cards and A♥ - denies A♣ and A
♦;    

---------------------------------------------------------------------------

Opener Responder
  1
        1♥
  2nt       3
♣  => NMF
   ?      After 3
♣ NMF Opener bids:
  3
♥ with 3♥ cards denying 4♥ cards, but can have 4♠, so
            if Responder bids 3nt this means Responder has 4
♥-4♠;
  3
♠ with 4♠ cards, denying support 3♥ cards;
 3nt to play - deny 3
♥ cards and 4♠ cards;
  4
♣ cuebid, 4♥ cards and A♣ and has 1º or 2º control in ♠;
  4
♦ cuebid, 4♥ cards and A♦ and has 1º or 2º control in ♠, no A♣;
  4
♥ support 4♥ cards, and has 1º or 2º control in ♠, denies A♣ A
♦;   
                 
Opener Responder
  1
♦        1♠
  2nt       3
♣  => NMF 
   ?    After 3
♣ NMF Opener bids:
  3
♥ shows 4♥ cards and may have support 3♠ cards that will be 
             bided if Responder bids 3nt showing has 4
♥-4♠;
  3
♠ support 3♠ cards and denies 4♥ cards;
 3nt to play, no support 3
♠ cards and no 4♥ cards;
  4
♣ cue bid - 4♠ cards and A♣, must has 1º or 2º control in ♥;
  4
♦ cue bid - 4♠ cards and A♦, must has 1º or 2º control in ♥; no A♣
  4
♥ cue bid - 4♠ cards and A♥, denies  A♣ A
♦;
  4
♠ support -4♠ cards and deny 1º and 2º control in ♥;  

When Responder has 5-5 in the majors he doesn't use NMF

Opener Responder
   1
♣      1♠
  2NT     3
♥ => 5♠-5♥
asking for support 3 cards major - If Opener has control in the minors and good top honors in both majors he may cuebid in 4
♣ as an invitation to slam.
--------------------------------------

Opener Responder
  1
        1♠
 2NT       3
♥ => 5♠-5♥
asking for support 3 cards major


How Responder bids with 6 cards in a Major and 10-11 hcp?

1- If the 6 cards suit have good top cards (AQJxxx / AKxxxx / KQ109xx)
  Responder can jump to level 3 asking for 2 cards support and maximum,
  when suit is weak like Q10xxxx or Kxxxxx try NMF to find information

O: ♠xx ♥A10x ♦KJx ♣KJ98x
R: 
♠AK7432 ♥Kxx 
♦xxx ♣x
Opener Responder
  1
♣      1♠
  1nt     3
♠ <= invitation
  pass  <= minimum, no support   

-------------------------------------------------  

O: ♠Qx ♥AJ10x ♦QJx ♣KJ9x
R: 
♠AJ10432 ♥Kxx Kxx ♣x
Opener Responder
  1
♣       1♠
  1nt      3
♠ <= invitation
  4
♠ <= maximum, honor support

-------------------------------------------------

O: ♠xx ♥A10x ♦KJx ♣KJ98x
R: 
♠AJ7432 ♥Kxx Qxx ♣x
♦
Opener Responder
  1
♣        1♠
  1nt       2
♦ <= NMF
  2nt       3
♠ <= invitation
  pass  <= minimum, no honor

-------------------------------------------------

O: ♠Jx ♥AJ10x ♦QJx ♣KJ9x
R: 
♠K97432 ♥Kx 
♦Axx ♣x
Opener Responder
  1
♣        1♠
  1nt       2
♦ <= NMF
  2
♥        2♠ <= asking for 2nd top honor
  pass                invitation or to pass 

--------------------------------------------------

O: ♠Axx ♥A10xx ♦KJxx ♣Q9
R: 
♠Q107432 ♥Kxx 
♦Qx ♣Ax
Opener Responder
  1
♦       1♠
  1nt      2
♣ <= NMF
  3
♥*     4♠
 pass              
 * Opener shows 4
♥ cards and
3
♠ cards support with a top honor.

--------------------------------------------------

O: 
♠Jx ♥AJ10 
♦♦Jx ♣KJ9x
R: 
♠K97432 ♥Kx 
♦Axx ♣x  
Opener Responder
  1
♣        1♠
  1nt       2
 <= NMF
  2nt       pass <= no good information

/ / /