[Poky]

What holds the opener?

1♣ - 1♥
1♠ - 1NT
3♦

[inquiry]

I can never recall using this specific auction. Interesting. Since opener could rebid 2♦ to force with 4-1-4-4 or 4-0-4-5 without the need to jump, we can eliminate all the monster hands with this distribution.

So this brings us to a group of hand like 4-3-1-5 and 4-1-3-5 where 3♦ could be somekind of fragment bid, or a hand where opener has a great club suit but is worried the responder would pass if he simply rebid 3♣. I think if opener had this latter kind of hand, he would have jumped to 2♠ instead of biddng 1♠.

So the choice for 3♦ falls between a fragment with three diamonds and fragment showing great hand and three card heart support. Since opener could rebid 3♥ over 1NT to show the three card heart support and imply diamond shortage, you might think this is the best use. But, 3♥ is not forcing. So, my thought is this should be a splinter in support of hearts (3 cards), showing a great hand, and is game force, but has not settled on a denomination yet. The splinter interprestion is also consistent with the rule if a simple rebid in a suit is forcing, then a jump rebid is a splinter.

The only alternative is bid 3NT with sure heart stopper, but you could go through 2♦ for that purpose.

[Fluffy]

I think 4306

althou it may be 4207 or 4108.