An operating system provides extensions through which application developers may extend the capabilities of a shell of the operating system. For example, application developers may add menu items to context menus for objects that are visible within an integrated system name space. In addition, developers may add property sheet pages for such objects. Application developers also have the option of providing per-instance icons for each instance of an object. Application developers may provide data object extension handlers for customizing data sources on a per-object class basis and may provide drop target extension handlers on a per-object class basis to customize drop target behavior. Developers may additionally provide copy-hook handlers to regulate file system operations on objects. Developers may also extend the functionality provided by the shell of the operating system by adding their own custom name spaces to the integrated system name space. The mechanism provided by the operating system to add such a name space is polymorphic and transparent to users.