Published on Tue Mar 01 2022
This will match an FEN string (https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation). It is not strict in having each rank separated by a '\' character, although it is strict in the order of characters for the Castling section. Anything not following the order of KQkq in the case where castling is available, will fail the Regex. It is also case sensitive for the Side and the "en passant" column letter.