PGN embedded command

PGN means Portable Game Notation, a text format for recording games. A PGN embedded command adds machine-readable data while remaining compatible with readers that understand only ordinary comments. It appears inside a brace comment governed by PGN comment syntax. The general form starts with [%, continues with a command name and parameters, and ends with ].

In {[%clk 1:05:23]}, clk is the command name and 1:05:23 is its parameter. The supplement documenting this convention proposes clk for recording the clock display after a move. It also describes several other time-related commands.

The convention comes from a supplement whose status is final draft, not from the original core PGN specification. The supplement deliberately avoids imposing one universal list of all possible commands. Interoperability therefore depends on the producer and reader assigning the same meaning to a command name.

Software that does not recognize a command should preserve it unchanged as part of the comment. This differs from a PGN tag pair, which stores descriptive data in the game's opening section rather than a command inside move-related commentary.