21. The non-transitory computer readable storage medium of claim 20 , wherein: a plurality of documents in the set of documents each have a resource locator; the instructions to group the set of documents into a plurality of clusters include instructions which, when executed by the one or more processors, cause the computer system to: order the set of documents in accordance with the resource locators; and select a respective plurality of consecutive documents from the ordering for inclusion in the respective cluster.
20. The non-transitory computer readable storage medium of claim 18 , wherein a respective document is determined to be related to one or more other documents in the respective cluster based on a resource locator of the respective document and resource locators of the one or more other documents in the respective cluster.