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I have added the ability to take back moves, and I have removed some more
bugs. Yesterday, the PBM was mailing the wrong URL to users. Instead of
putting your userid in the URL, it would put your opponent's there. That
is now fixed. I also fixed how it displays movelists with branches.

To take back moves, use the drop down menu displaying the movelist to go
back to the last move you want to keep in the game. This should be one of
your opponent's moves, not one of your own. Although the menu is supposed
to disable all of your past moves in the list, Internet Explorer ignores
this. I'll have to change it so that selecting one of your moves takes
you back to one of your opponent's moves. The last move should be one of
your opponent's moves, so that the next move will be yours. You should
not just select the past move in the menu; you should click the 'Go'
button to go back to it. Once the board is updated, you can make a new
move from that point in the game. When you verify your move, your new move
will appear at the end of the movelist, and all moves between it and the
move you went back to will be branched out of the main game. They will
still appear in the movelist, but your new move will now continue the main
branch of the game.

The ability to take back moves is still buggy. I expect to continue work on
it tonight.

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.

One thing to note about the PBM is that it requires UserIDs and will not
work with PersonIDs. When I tried inviting myself by my PersonID,
FergusDuniho, it told me that this ID had no email address associated with
it. This presents a problem for anyone who would like to start a game,
because for those of us with PersonIDs, it is our PersonIDs, not our
UserIDs, that show up with our names in the Comments area. Until we can
find some solution to this, you should invite people to play by email
address instead of userid or first ask someone you would like to play
against what his UserID is.

I think the PBM is now ready for general use. The most important new
features have been added, and these seem to be working fine. These include
use of UserIDs to identify players, logging of games, facilitation of
real-time play, the use of graphic images as backgrounds for boards of
unusual design, and the ability to take back moves without subtracting
anything from the log. Are there any other features anyone would like the
PBM to have?

For those of you who don't already know where the PBM is, it is at:

http://play.chessvariants.com/pbm/play.php

It is a web-based play-by-mail system for playing Chess variants with
other human opponents on-line. It does not provide computer opponents, and
it does not enforce rules.

For the purpose of inviting an opponent to a game, the PBM will now accept
a PersonID. When it gets a PersonID, it will convert it to the
corresponding UserID. So now you don't have to know someone's UserID to
invite him to play. You can use either PersonID or UserID and get the same
results. Thanks go to David Howe for supplying me with the database code I
needed.