The Interactive Diagram solves the castling problem by adopting the general convention that left and right for black should be interpreted in the context of the symmetry parameter; for symmetry=mirror they should be flipped. Before that I had an explicit parameter castleFlip, but this is now automatically set according to the value of symmetry, if no explicit value was given. In fact it would be best if there was left-right flip for all moves in that case, but I haven't gotten to implementing that, as pieces with left-right asymmetry are very rare, and the few (Shogi) variants I am aware of that do have them use symmetry=rotate rather than mirror.
I think ccN would only be useful as part of a multi-leg move, because it is not just an abbreviation for cabN. The latter would force you to capture the a piece on the detour, and if there was no enemy piece there, would not allow the move. The idea of ccN would be that it must make the detour if there is something to capture, but can be ignored if there isn't, so the remainder of the move can still be made. So apart from standing for cabN, it would also allow mabN (detour over empty square), oabN (in case the detour would leave the board) and dabuN (hop over a friendly piece, disguised as destroying it and then putting it back on the same square). In this meaning an isolated ccN would not just allow rifle capture, but also a turn pass in case there was a friendly piece, empty square or board edge within Knight range. This is almost certainly not what you'd want. But in a multi-leg context such as [Q-fccK] it would describe the Advancer: move as Queen to an empty square, and mandatorily remove an enemy on the next square if one is there, but never mind if there isn't such an enemy (or such a square), and doe the Q leg anyway.
The Interactive Diagram solves the castling problem by adopting the general convention that left and right for black should be interpreted in the context of the symmetry parameter; for symmetry=mirror they should be flipped. Before that I had an explicit parameter castleFlip, but this is now automatically set according to the value of symmetry, if no explicit value was given. In fact it would be best if there was left-right flip for all moves in that case, but I haven't gotten to implementing that, as pieces with left-right asymmetry are very rare, and the few (Shogi) variants I am aware of that do have them use symmetry=rotate rather than mirror.
I think ccN would only be useful as part of a multi-leg move, because it is not just an abbreviation for cabN. The latter would force you to capture the a piece on the detour, and if there was no enemy piece there, would not allow the move. The idea of ccN would be that it must make the detour if there is something to capture, but can be ignored if there isn't, so the remainder of the move can still be made. So apart from standing for cabN, it would also allow mabN (detour over empty square), oabN (in case the detour would leave the board) and dabuN (hop over a friendly piece, disguised as destroying it and then putting it back on the same square). In this meaning an isolated ccN would not just allow rifle capture, but also a turn pass in case there was a friendly piece, empty square or board edge within Knight range. This is almost certainly not what you'd want. But in a multi-leg context such as [Q-fccK] it would describe the Advancer: move as Queen to an empty square, and mandatorily remove an enemy on the next square if one is there, but never mind if there isn't such an enemy (or such a square), and doe the Q leg anyway.