A user interface (132)--be it graphical (GUI) or telephony (TUI) to an application (120) is defined by stored interface and feature description documents (122,124) written in XML and JavaScript, so that the user interface and changes thereto can be effected without access to source code. Interface description documents define the appearance and the behavior of the user interface toward the user, while feature description documents define the interaction of the user interface with the interfaced-to application, both in conformity with a user-interface object model (310). Stored connector object plug-ins (126) define connector objects for rendering elements of feature description documents, and stored layout object plug-ins (128) define layout objects for rendering elements of interface description documents of one or more interfaces.