Changes

The earlier [https://en.wikipedia.org/wiki/X-FEN X-FEN] extension was introduced by [[Reinhard Scharnagl]] in 2003, and covers not only [[Chess960]] but also 10x8 variants. Its author dogmatically claimed upward compatibility with standard chess <ref>[https://www.stmintz.com/ccc/index.php?id=437213 Why to use compatible X-FEN (in Chess960)] by [[Reinhard Scharnagl]], [[CCC]], July 17, 2005</ref>, still using the '''KQkq''' [[Castling Rights|castling right]] characters for all Chess960 positions where the king is between both rooks - and the [[Files|file characters]] otherwise. Further, X-FEN introduced a changed [[En passant|en passant]] target square semantic, which is only specified after a double pawn push was made beside an opponent pawn that might capture en passant if legal, that is not leaving its king in check.