Abstract: An application development system, optimized for authoring multimedia titles, enables its users to create selectively reusable object containers merely by defining links among instantiated objects. Employing a technique known as Hierarchical Encapsulation, the system automatically isolates the external dependencies of the object containers created by its users, thereby facilitating reusability of object containers and the objects they contain in other container environments. Authors create two basic types of objects: Elements, which are the key actors within an application, and Modifiers, which modify an Element's characteristics. The object containers (Elements and Behaviors--i.e., Modifier containers) created by authors spawn hierarchies of objects, including the Structural Hierarchy of Elements within Elements, and the Behavioral Hierarchy, within an Element, of Behaviors (and other Modifiers) within Behaviors.