1♦ - 1♠
1NT - 2♣*
2♠ - 4♠
*NMF
In this hand NS have reached 4♠ and declarer must pick up the ♥ suit for 3 winners to make. EW play coded leads meaning East leads the 9 from QT9x. On this deal therefore coded leads lose as the lead of the 10 denies the Q and the ♥ position becomes immediately known to declarer. He can comfortably play to drop the Q♥ doubleton.
Here is my idea for "hyper-coded leads" - it's probably been thought of before but I've never heard of anything like it:
Both defenders have information that declarer doesn't on this hand, that is the split of the trump suit since the auction shows that the opps have exactly 8. It is therefore possible on hands like these to further code your leads. For example, when leader has an odd # of trumps he can lead the 9 from this suit and when he has an even number he can lead the 10. That is just an example but it demonstrates the principle I'm trying to indicate which is that the ♥ position then becomes evident to the defence but not to declarer since at that point he is unaware of the ♠ split. When East gets in again with the A♠ he can lead another ♥ and force declarer to guess.
I hope that all makes sense. Is this implementation legal or even useful? I have my doubts because I've never come across any discussion about it. Obviously it could only be used when the defenders have an exact count of the opps trumps from the auctio,n but like I say it is the principle I am theorising about.