Development of multiple-version software employs versioned documents in a store. The documents are compared (differenced) at both line and character levels. Potential conflicts in merged documents are marked by detecting possible alternative histories from a common parent document. Changes from an earlier version are removed from a later version of the same document even when the document has intervening versions. A build lab allows developers to work in parallel on a new software build while another build is being run and patched on a different set of documents; the developers each have private copies from which changes pertaining to a build have been added, and then backed out when the file is returned to a common area.