> The tetrominoes spawn horizontally and with their flat side pointed down.
> Terms used in the user manual: "Tetriminos" not "tetrominoes" or "tetrads" or "pieces", letter names not "square" or "stick", etc.
The spec doesn't meet the spec.
The spec is not the user manual, so it's okay ;)
Interestingly, the #1 hit for Tetris on Google is freetetris.org which is endorsed with the Tetris trademark, yet it does not follow these guidelines. For example the pieces do not start "with their flat side pointed down".
When I was coding a Tetris clone as my standard exercise to learn a new programming language I found this site to be very useful: