Applications have a user interface that can take a variety of different forms. One common user interface includes menus and toolbars. On a computer system, each application program can have its own user interface which appears when the application program is executing. An application may also be a composite application consisting of multiple, different application programs. Each of the different application programs may be a component of the composite application. The composite application may present to a user a single common interface for all the component application programs. With this single interface, all the application programs of the composite application may share the same command menus and toolbars. A single user interface for the composite application may be shared between all the application programs. One drawback of the foregoing is that each application program contributing to the single user interface may be developed independently of the other application programs of the composite application. In such instances, the user interface for each program of the composite application may require a collaborative effort while the remaining portions of each application program are independently developed.