Tools which provide graphical editing techniques for the design of user interface presentations are increasingly commonplace. Such tools vary widely in the mechanisms used to define user interfaces and while some are general purpose, others are targeted at particular application domains. Designers faced with varying requirements must choose one tool and live with its shortcomings, purchase a number of different tools, or implement their own. The paper describes an approach to facilitating the latter by providing a library of augmented user interface components called MOG objects which embody both end-user and editing semantics. User interface design tools based on this approach need only provide mechanisms for composing MOG objects into user interfaces and the addition of any other, higher-level functionality. MOG-based user interfaces retain an in-built editing capability and are inherently tailorable.