1. A method comprising: storing, in an index associated with a system, a first index entry associated with a first collection item; storing, within the system, data that indicates that a plurality of items indexed by the system are collection items, wherein the plurality of items include the first collection item; in response to receiving a search query, identifying a set of matching items, wherein the set of matching items includes one or more base items and the first collection item, wherein identifying the set of matching items includes matching the search query to the first index entry; and responding to said search query by generating search results based at least in part on the set of matching items, wherein the search results comprise: a) at least one of the one or more base items; and b) the first collection item; wherein the method is performed by one or more computing devices.