3Leaf have posted an initial draft of their spec for Arcs of Fire and the Tablet PC SDK:
http://ea.3leafdev.com/2004/12/draft_version_o.html
Check it out here.
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p class=ngrelatedlinks> The key seems to be the development of pen “trajectory” classes, which will presumably provide high-level abstractions of “fast stroke,” “slow stroke,” “smooth curve starting near this and pointing towards that.”