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I don't mean iWork docs but for example personal docs in GoodReader iCloud folder and perhaps Mac OS ~/Library/Mobile Documents.

Is there any official documentation about it?

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up vote 4 down vote accepted

Delta. It splits this intelligently into chunks and only updates the relevant chunks using Rabin fingerprinting.

You can see this in Apple's WWDC iCloud presentation, and slides.

A pretty good description of this chunking can be seen in Siracusa's Lion review, however the review describes this process in terms of document versioning, but the fundamentals are the same.

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I think that it is full file sync. The delta aspect that you are wondering about would be with Versions (or Time Machine), and that is a separate set of functionality beyond the scope of iCloud's Documents.

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Can you provide a source to back this up? – Nathan Greenstein Feb 26 '12 at 21:27

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