1. A computer-implemented method for collecting information about a group of documents, comprising: under control of one or more computer systems configured with executable instructions, seeding the group of documents with one or more seed documents; identifying, in at least a portion of the group of documents, at least one reference to at least one secondary document; adding to the group of documents at least one secondary document obtainable using the identified at least one reference; identifying, for at least a portion of the documents in the group of documents, two or more attribute values associated with at least one aspect of the document; adding at least a portion of the identified attribute values to a set of information associated with the group of documents, the set of information enabling documents in the group of documents to be located based at least in part upon any of the attribute values in the set of information; applying a test to at least one secondary document; and adding the attribute values identified for the at least one secondary document to the set of information associated with the group of documents only if the applied test is satisfied.