The coordinate system used by this server is [A...Z][1...25], depending on the board size. 'I' is not a valid letter. The maximum board size is 25.
On a 19x19 board A1 is upper left, T19 is lower right, D4 is a Star Point.
Blacks first move can be the handicap: Handicap #, where # is the number of stones. # has to be between 2 and 9 inclusive.
During the game pass is also a valid move. It takes 3 passes to score a game. (See match)
Undo is also valid during a game and during scoring.
See also: match undo