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{mods: {mods converted to JSON}, collection: collection_id, derivatives: [location_of_derivatives], private: [Boolean] <Boolean, default=false> }
GET returns the mods (or otherwise specified subset of metadata), POST requires everything to be able to create a new item, PUTS updates just the supplied JSON. POST and PUT fail if there is not: mods, a unique pid for the object, valid collection_id, mods, and derivatives. If private is not specified, it is assumed to be public.
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