docs for ICP versions 3,4?

There was a talk at the recent caching workshop in Poland that mentioned
that there are versions 3 and 4 of the ICP around, 3 being used by Harvest
version 2+.

Does anybody have pointers to docs on these protocol versions? I didn't
find any on the Harvest pages (netcache.com) or on the Squid pages.

Thanks,

Andreas

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