In Philadelphia, a deal showed a rare example of the handling of the empathetic splinter matrix via a flag to identify the fit suit.
My LHO had opened 1NT (strong), and partner doubled to show (a) both minors, (b) just diamonds, (c) both majors, or (d) some other very strong hand otherwise unbiddable. After a pass from RHO, holding Kxx-Jxxx-xxxx-Ax, I advanced 2D, as my normal "first duty" was to pick the preferred minor.
Opener made a shocking rebid of 3D, and partner doubled, showing both majors and extras.
At this point, I have an incredibly valuable hand. Thinking along the empathetic splinter matrix, hearts is the "4-4 fit suit," with 5-4 being of course acceptable (and preferable after a 1NT opening by the opposition). Spades is the 5-3 side source. Clubs the "ace only" side; and diamonds clearly contextually the short suit.
Contextually, the matrix is known, except that partner cannot know which is the 4-4 and which is the 5-3. Thus, in this sequence, I opted 4C, a flag for hearts indicating that the matrix was as it was.
Partner held Axxxx-AKxxx-void-Jxx and just enough for the slam. With the 3D call by Opener, Opener was likely to hold 2-2-6-3 shape (he in fact held 2-2-5-4), which meant that both hearts and spades were cooperating. As long as partner made sure to right-side the contract by forcing me to bid hearts first, the slam was unstoppable; LHO held the King and Queen of clubs. (On a small club lead, hop Jack. On a club honor lead, win the Ace and then lead a club toward the Jack, establishing a pitch for the third spade.)
In the World Open Pairs, no one reached this slam.
This same concept may apply in other sequences where (a) one partner has shown a two-suiter, (b) a specific known suit is clearly the short suit contextually or by definition, and (c) no one has been able yet to define fits. For example assume for the sake of argument that a 3C response to a 1NT opening shows 5-5 majors and invitational. Assume, for example, that after a 1NT opening and a natural 2C or 2D overcall, 3H by Responder shows 5-5 majors and game-invitational; in that sequence, Opener's 4C or 4D would seem to be empathetic flags.