On IA, a collection is a type of item that groups other items. They can only be created by authorized people, generally staff, and serve as the primary organizing method for structuring groups of items. Collections can be nested, and items can be in multiple collections, forming a graph (which may include cycles).
An item is included in a collection by specifying the collection identifier as a value of the collection metadata key for the item. This can be repeated to include an item in multiple collections.
Another method for including items in a collection is by specifying the search_collection metadata key on the collection, with a search query as the value. Then all the items matched by that search query will be included in the collection, although the backlink from the item to the collection won't show up.
There are large, overarching collections (like texts ) and specific collections for an institution or type of item, like bostonlibrary or nationalknittingmagazine. Some collections also have magic effects, including making the items accessible only to logged in users (loggedin), geo-blocked (geo_restricted), throttled (highbandwidth) or disabling the download view (stream_only).
The overarching collections are: