8. A system comprising: one or more processors; and a non-transitory machine-readable storage medium coupled to the one or more processors, the non-transitory machine-readable storage medium comprising instructions that, when executed by the one or more processors, implement operations comprising: detecting a request for provision of a first document that is available for provision, updating a count of referrals based on determining the request was sent from a set of one or more networks, the count of referrals comprising a number of requests for provision of the first document, retrieving a second document based on the first document and on the count of referrals transgressing a threshold value, and providing the second document in response to a subsequent request for the first document, the subsequent request occurring after expiration of an availability of the first document.
8. A system comprising: one or more processors; and a non-transitory machine-readable storage medium coupled to the one or more processors, the non-transitory machine-readable storage medium comprising instructions that, when executed by the one or more processors, implement operations comprising: detecting a request for provision of a first document that is available for provision, updating a count of referrals based on determining the request was sent from a set of one or more networks, the count of referrals comprising a number of requests for provision of the first document, retrieving a second document based on the first document and on the count of referrals transgressing a threshold value, and providing the second document in response to a subsequent request for the first document, the subsequent request occurring after expiration of an availability of the first document. 13. The system of claim 8 , wherein the operations further comprise: identifying a plurality of references based on the first document, the plurality of references associated with documents that are similar to the first document; and providing one or more of the plurality of references within the second document.