Sentinels and whose turn

Chess.sol

contract Chess {
  /// The top/bottom rows and left/right columns are treated as sentinel rows/columns for efficient
  /// boundary validation (see {Chess-generateMoves} and {Chess-isValid}). i.e., (63, ..., 56),
  /// (07, ..., 00), (63, ..., 07), and (56, ..., 00) never contain pieces. Every bit in those rows
  /// and columns should be ignored, except for the last bit. The last bit denotes whose turn it is to
  /// play (0 means black's turn; 1 means white's turn). e.g. a potential starting position:
  ///                                Black
  ///                       00 00 00 00 00 00 00 00                    Black
  ///                       00 03 02 05 06 02 03 00                 ♜ ♝ ♛ ♚ ♝ ♜
  ///                       00 01 01 01 01 01 01 00                 ♟ ♟ ♟ ♟ ♟ ♟
  ///                       00 00 00 00 00 00 00 00     denotes
  ///                       00 00 00 00 00 00 00 00    the board
  ///                       00 09 09 09 09 09 09 00                 ♙ ♙ ♙ ♙ ♙ ♙
  ///                       00 11 12 13 14 12 11 00                 ♖ ♘ ♕ ♔ ♘ ♖
  ///                       00 00 00 00 00 00 00 01                    White
  ///                                White
}