Workplace Shell application development involves subclassing existing classes, introducing new methods as well as defining behavior for overridden Workplace Shell methods. In writing these method overrides, it is important to keep in mind that they may be invoked from other threads. For example, an override of wpPopulate will be invoked on an object of a WPFolder subclass, when wpOpen or wpViewObject is invoked. As described in "The Populate Thread" section, wpPopulate is sometimes invoked from the Populate thread.