Check if the piece lie within the board.

def validate_coordinates(self, x, y):
        """ Check if the piece lie within the board. """
        if not(0 <= x < self.length and 0 <= y < self.height):
            raise ForbiddenCoordinates(
                "x={}, y={} outside of {}x{} board.".format(
                    x, y, self.length, self.height))