Source and Article references in: BridgeGuys
This is a variation of the Jacoby 2 No Trump used in limit raises.
The following chart provides the responses of the responder and the rebids of the opener:
North South Meaning 1 any Major 2NT Swedish Jacoby 2 No Trump 3 Indicates a minimum opening. 3 Promises extra values with no singleton. 3 Promises extra values with no Club singleton. 3 Promises extra values with no Diamond singleton. 3NT Promises extra values with a singleton in the unbid Major suit. 4 Promises extra values and a void; also viewed as asplinter bid. 4 Promises extra values and a void; also viewed as asplinter bid. 4 other Major Promises a void in the unbid Major suit.
The bidding process becomes clear after such descriptive responses and the opener and the responder can both bid accordingly as illustrated in the following example.
North South Meaning 1 any Major 2NT SwedishJacoby 2 No Trump 3 Indicates a minimum opening. 3 bid Major This is asign-off bidby the responder. Partner must pass except when holding additional game of slam values. 3 This is anasking bidfor any singleton. 3 This is acuebid, but only in the opening bid is Spades. 3 This is acuebid, but only in the opening bid is Hearts.
If the bidding sequence is as follows, then the rebids by the opener are indicated in the following chart:
North South Meaning 1 any Major 2 NT SwedishJacoby 2 No Trump 3 Indicates a minimum opening. 3 This is anasking bidfor any singleton. 3 Promises a singleton Club. 3 Promises a singleton Diamond. 3NT Promises a singleton in the unbid Major suit. 4 Indicates no singleton and is a cuebid of Diamonds. 4 Indicates no singleton in any suit; cuebid not possible.
If the partnership agreement is such that these responses are employed, then the first response of 2 No Tump can be applied even on invitational values. As a consequence the bidding sequence 1 Major – 3 Major becomes preemptive in nature.