Single Comment

The PBM seems to be working well now. The ability to take back moves is now
available, though it limits the moves you can take back. Here is how it
works. First, you go back to a move by your opponent, then you make a new
move. Your new move gets appended to the end of the movelist, and all
moves between your new move and the one you went back to get branched off.
This means that their level number will be incremented, and this will show
up in the movelist as an extra '|' in front of each line that is part of
this branch. They are no longer part of the main branch of the game,
though they remain in the movelist for the sake of a complete record of
the game.

Here are the limitations on taking back moves. You cannot go back to any
of your own moves, because the next move would not be yours. You also
can't go back to a move within a closed-off branch. This prevents
corruption of the moves tree. When a series of moves gets branched off,
the movelist is set up so that no subsequent moves can be part of that
branch. Any attempt to get around this would corrupt portions of the
movelist. So the only moves you can take back are those in the game's
main branch. This is the level 0 branch, which has no pipes (|) in front
of its lines.

The moves you can't go back to are disabled in the menu. In case your
browser ignores the DISABLED keyword, there is a JavaScript function
running to prevent the disabled options from taking you anywhere. And in
case you don't have JavaScript, the PHP code tells you to go back when
you do try to go to a point in the game from which you can't make a new
move.