1. A multi-document editor system comprising: a repository storing a plurality of documents having code fragments, the code fragments comprising switchable code fragments that can be switched in and out during runtime by a switch framework; a graphical user interface having a single editor window within a display region, the single editor window for concurrently displaying a rendering of the plurality of documents, at least some of the plurality of documents being sub-documents of a parent document, the single editor window also displaying comment lines surrounding respective documents of the plurality of documents, the comment lines being non-editable; a program editor module that provides a unified editor control to the editor window for editing each of the plurality of documents in the single editor window, the unified editor control providing a control function for disabling the comment lines, the program editor module executing a line refactoring process to set break-points in the parent document in relation to specific sub-documents; and an interface builder module that automatically generates an interface for a business application that is created using the program editor module, the business application using the plurality of documents and being generated such that the business application can be run without local customization and can run in both centralized and distributed client/server configurations.