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, the search query comprising one or more criteria that a user has explicitly entered, and the search query having an association with a topical area for a search, (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 entire query such that each responsive document includes each of the one or more criteria of the search query, (5) retrieving a definition of a search space, the definition of the search space comprising one or more normalized citations to every document within the search space, and the search space having an association with the topical area for the search; (6) filtering the responsive documents resulting from the execution of the search query by checking each responsive document against the definition of the search space and removing from further consideration an responsive document not found in the definition of the search space; and (7) provide information that identifies one or more of the remaining 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.