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PDN Extensions

Embedded commands

Comments in PDN files may have embedded commands. Embedded commands may appear anywhere inside comments, and they have the following syntax: [%COMMAND VALUE], where COMMAND identifies the command and VALUE is command-specific syntax.

clk, mct, egt and emt command

The following commands are taken from [DGT]:

Command Description
clk Time displayed on a clock (remaining time)
mct Time displayed on a clock (elapsed time)
egt Elapsed game time
emt Elapsed move time

The values of the clk, egt, emt and mct commands are in h:mm:ss format. Usually clk values come from a digital clock, while mct values come from a mechanical clock.


1. 31-26 {[%clk 1:55:21]}

clock command

The clock command is an extension of the clk command. An embedded clk command should match with the following regular expression:



1. 31-26 {[%clk w0:00:10 B0:00:03]}

23.44-39 {[%clk 1:05:23]} 18-23 {Optional leading comments
[%clock 0:49:11] optional trailing comments}

In cases like this the clock time is connected to the preceding move. It is the preferred way of specifying clock times during live recordings with electronic boards. A clock command may contain one or two clock times. Each of them may be preceded by a w or a b to denote the clock time for white or black. If uppercase is used, it means that the clock for this player is running.

Setup commands

The PDN grammars presented in this document contain an extension for doing setups of a position anywhere in the game. The motivation for having this command is threefold:

  • It gives a well-defined way to handle illegal moves, that happen occasionally in tournament practice.
  • They can be used to handle move recognition failures of electronic board software.
  • In game analysis it is common to make side steps to different positions, for example to a similar position that has occurred before. The setup command allows to incorporate these side steps as normal variations starting with a setup.

A setup command is a FEN setup command surrounded by forward slashes. Note that this extension is not backward compatible with older versions of the PDN standard. This is an intentional choice, since the moves which appear after a setup are ill-defined if the setup is ignored. Setups are changes on the board, and so they should be on the same level as moves. It is therefore not a good idea to model them as embedded commands inside comments.

Null moves

For programmers, null moves are sometimes useful to denote an empty move. A possible notation for a null move, proposed by Gérard Taille, is

/FEN "B::"/


1.31-26 17-21 /FEN "B:B1-16,18-21:W26,28,33-50"/
{ White forgot to make a capture and played 32-28 instead }

Suppose a game starts with an illegal move, resulting in the following sequence of positions:

_images/setup1.png _images/setup2.png _images/setup3.png

This can be encoded using

/FEN "W:W31-50:B1-20"/
/FEN "B:W28,31,33-50:B1-18,20"/
01... 14-19

The setup of the initial position is required here. If it was omitted, the second setup would be taken as initial position of the game.