1. A computer system for identifying one or more electronic documents within a collection of electronic documents, the system comprising: one or more processors programmed at least to (1) store, in a memory operatively coupled to at least one of the processors, a search level that is a whole number that is at least two, (2) accept a search query through an interface operatively coupled to at least one of the processors, (3) define a subset of a collection of electronic documents, the subset comprising a plurality of electronic documents, (4) execute the search query against all documents in the subset, thereby identifying as responsive documents all documents in the subset that satisfy the query, and (5) provide information that identifies one or more of the responsive documents through an interface operatively coupled to at least one of the processors; wherein the subset comprises one or more source documents within the collection and one or more additional documents within the collection, the one or more additional documents being identifiable by a process carried out for a number of iterations equal to the search level and comprising (1) a first iteration that comprises finding one or more references in one or more of the electronic source documents, each of the references identifying a respective document in the collection, and adding to the subset each document in the collection that is identified by any of the found references but is not already in the subset, and (2) one or more subsequent iterations, each of which comprises finding one or more references in one or more of the documents added to the subset in the immediately previous iteration, each of the references identifying a respective document in the collection, and adding to the subset each document in the collection that is identified by any of the found references but is not already in the subset.