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Specifying chess variants in Sjaak
Sjaak comes with a number of build-in variants, but it's also possible to create your own without having to modify the program. Since revision 367, Sjaak comes with a "variants.txt" file, which contains a detailed description of how to define a variant as well as a number of examples.
To make the variants work in XBoard/WinBoard, all you have to do is specify the name of the file after the engine command:
You may need to enclose the entire command in quotes, and you may need to specify the full path to the file in order for Sjaak to find it. If the file is found succesfully, the variants listed in it will appear in Sjaak's option dialog box as variants that can be played as variant "fairy".