Tetris Guideline

The Tetris guideline is the current specification that The Tetris Company enforces for making all new (2001 and later) Tetris games alike in form. A mode labeled "standard" or just plain "Tetris" will adhere to the Guideline more closely than other modes.

Current rules include:
 * 22x10 cell playing field
 * Tetromino colors
 * Cyan I
 * Yellow O
 * Purple T
 * Green S
 * Red Z
 * Blue J
 * Orange L
 * "Bag" randomization of tetrominoes
 * Tetrominoes are generated 7 at a time as a permutation. (There are 5,040 different such permutations.) This means that only 12 tetrominoes can come between one I and the next I, and a run of S and Z tetrominoes is limited to 4.
 * Tetromino spawn locations
 * The I and O spawn in the middle columns
 * The rest spawn in the left-middle columns
 * The tetrominoes spawn horizontally and with their flat side pointed down.
 * Tetromino rotation and lockdown behavior (see SRS)
 * "Hold piece": The player can press a button to send the falling tetromino to the hold box, and any tetromino that had been in the hold box moves to the top of the screen and begins falling. Hold cannot be used again until after the piece locks down.

The combination of hold piece and bag randomizer would appear to allow the player to play forever.