The extensions of SGF that I use in SmartGo Kifu and SmartGo Books, what I call SGF Kifu, are still in flux. However, some parts I expect to remain quite stable, and I have documented those. You can find the current version at:

http://smartgo.com/pdf/sgfkifu.pdf

Hope this answers more questions than it raises, and will be helpful for those trying to create rich Go content. Any questions or issues, let me know.

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Anders Kierulf
@smartgo

Thanks Anders!

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Dave Sigaty
"Short-lived are both the praiser and the praised, and rememberer and the remembered..."
- Marcus Aurelius; Meditations, VIII 21