Not only kings can be mated, but other pieces can too. Any piece that is attacked, but which cannot escape capture by moving away, capturing the attacking piece, or interposing the attacking piece is considered to be mated, and is removed from the board. Note that such a move does not need to be played: when a piece is attacked, and it can escape capture using normal chess rules, it is not removed.
Pieces cannot be taken in the normal way, only by the `mate-capture', as described above. Also, check is ignored: kings and other pieces may be placed on a position where they are in check.
When multiple pieces are mated, they are all captured. The moving player decides in what order mated pieces are removed. If removing a mated piece causes further pieces -- of either side -- to be mated, then these pieces are removed as well.
Capture is not optional, but if a mated piece is missed by accident, the other player decides whether to ignore the mate or to return the game to that point.
Purpose of the game is to `mate-capture' the king of the opponent.