C/CIF - Chess Interchange Format
CIF - Game Information
The attribute id is a reference to a game header defined inside the index section of the archive. If a game reference is given, then no other attribute in this game should be set, because the game header in the index section is already containing these attributes. Also note that this game is inheriting not only the attributes from the game header in index section, it is inheriting all the elements defined in the referenced game header. Further note that this attribute is mandatory if the archive contains an index section.
Attribute signature should not be set to any other value than ":PGN" if it is not guaranteed that the move data section contains valid data (any move is either valid/legal or the appropriate flag is set). If the signature is not specified, or if the signature is ":PGN" than the reader of the archive has to check the validity/legality of each move, otherwise the reader can trust that the move data is correct. Note that this attribute will be overruled from the attribute creator given in the archive information section. If the creator is not empty, and not set to ":PGN", and none of the attributes modifiedby is set to ":PGN", than any game inside the archive contains valid move data (the writer of the archive has to guarantee this). Note: if the archive contains an index section, then both elements, the index game entry, and the game data element, must contain the same signature.
Unusual or very specific game information will be stored inside tag/value pairs in element tags. This is also the appropriate place for private game information.
Note: if this game is referencing a game header inside the index section of the archive, then these elements should not be repeated here. Also it is not allowed to overwrite elements which are already defined in the referenced game header. But it is allowed to define additional elements which are undefined in the referenced game header.
Extension for Tandem chess games (Bughouse)
A tandem chess game contains either zero or two player sections, either zero or two opening sections, and either zero or two extraneous sections. The first one belongs to the first board, and the second one belongs to the second board, respectively.
Furthermore for each board a separate tag section is required, and also separate game flag sections. The first one belongs to the first board, and the second one belongs to the second board, respectively.
