17. A computer program product comprising a computer-readable storage medium encoded with instructions that, when executed by at least one processor within a computer system that comprises one or more processors and a memory operatively coupled to at least one of the processors, cause the computer system at least to: store in the memory a search level that is a whole number that is at least two; store in the memory a definition of a subset of a collection of electronic documents, the collection of documents comprising a plurality of documents, and the subset comprising 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; receive through at least one interface operatively coupled to at least one of the processors a definition of 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; identify all responsive documents within the subset that satisfy the one or more criteria comprised by the search query such that each responsive document includes each of the one or more criteria of the search query, and retrieve 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; filter 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; transmit through the at least one interface information for display the user that identifies one or more of the remaining responsive documents.
17. A computer program product comprising a computer-readable storage medium encoded with instructions that, when executed by at least one processor within a computer system that comprises one or more processors and a memory operatively coupled to at least one of the processors, cause the computer system at least to: store in the memory a search level that is a whole number that is at least two; store in the memory a definition of a subset of a collection of electronic documents, the collection of documents comprising a plurality of documents, and the subset comprising 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; receive through at least one interface operatively coupled to at least one of the processors a definition of 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; identify all responsive documents within the subset that satisfy the one or more criteria comprised by the search query such that each responsive document includes each of the one or more criteria of the search query, and retrieve 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; filter 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; transmit through the at least one interface information for display the user that identifies one or more of the remaining responsive documents. 19. The computer-readable storage medium of claim 17 , wherein the search query is a Boolean query that the user has entered.