If you are an OS/2 user, you are familiar with the Workplace Shell. The shell provides many objects, including folders, programs, and special-purpose objects such as the shredder. You can manipulate objects with actions such as double-click and dragging and dropping one object on another. These actions send messages to the shell objects. For example, double-click sends a "wpopen" message. Objects respond to these messages by running methods that perform the requested actions. The class of the object receiving the message determines the method used for each action; therefore, opening a folder does something different than opening a program.