Changes

a) * piece placement: similar to chess. Use x/X for dark Jeiqi piecesb) * captured pieces: all revealed captured pieces and their numbers, enclosed by brackets []. This part appears immediately after the first part, without any space. Pieces with no capture are ignored. Jeiqi pieces are not compulsory since we can calculate them from the board and revealed captures. That can make the FEN string a bit shorter, avoid redundancy and inconsistent data, avoid ugly using due to 2 -digit numbers (Jeiqi pieces could be 15 - two-digit numbers). Empty brackets could be omitted too. Pieces can be placed in any order. For being beautiful, it is suggested to list all-white pieces first, descending by piece values.

* Jeiqi pieces don’t use Jeiqi symbol (X) but their fake pieces. That is just for solving ambitious cases. For example, if the move is written as “x9.1=c” we don’t know if that is a move of a fake Pawn or a fake Rook at column 9. However, “r9.1=c” says clearly the fake Rook at column 9 moved and revealed into a Cannon. The move of a Jeiqi piece and a revealed pieces one can be easily distinguished by checking if they are revealing. For example, even if there are two black Rooks in is a Rook at column 9advanced 1, their moves can not it’s move should be ambiguous since r9“r9.1 is definitely by revealed Rook and r9.1=c is definitely by the Jeiqi one1”.

Inform a engine it can play Jeiqi variant:

'''bestmove:''' as typical but it could not have a revelational piece even the moving piece is a dark Jeiqi one. Reason: the engine cannot decide that about revealed piece: