There are many challenges that software developers face during the development of complex User Interfaces (UIs). Desired behaviour may be autonomous or reactive, and possibly real-time. Each UI component may be required to exhibit a radically different behaviour from that of any other component, and the behaviour of components may be inter-related. These complex behavioural relationships between components are often difficult to express, and are even more difficult to encode and maintain. A solution may be found in Model-Driven Engineering. In particular, Statecharts, a formalism for describing complex, reactive, timed, state-based behaviour, is highly suited to model UI behaviour. At the same time, SVG, in combination with ECMAScript is becoming increasingly popular as a platform for application development. The ECMAScript language is used to implement interactivity and dynamic behaviour in SVG visual objects. It is thus possible to create browser-based, SVG UIs which are rich in both their visual appearance and in their interactive behaviour.