How are the levels of backgammon organized...

The levels of backgammon, from bottom to top, are: 10th, 9th, 8th, 7th, 6th, 5th, 4th, 3rd, 2nd, 2nd, 1st, 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th. Forbidden moves are only for black on the advance side. There are three-three forbidden moves, four-four forbidden moves, four-three-three forbidden moves, and long-linking forbidden moves.