As the user uses a metaphor to mesh his or her mental model with an application, the metaphor may lead to misunderstandings about the capabilities of the software. This is the surface of the interface, its operational characteristics. The desktop and the equivalence between finger-pointing and direct manipulation are examples of this. This includes the operations, objects, and relationships within the application. Metaphors can be both limiting and liberating.
Literal features enhance an interface's learnability.
Magical features are defined to be those capabilities that deliberately violate the metaphor in order to provide enhanced functionality. This can result from conscious and valid choices, as well as from an inability to implement a complete metaphor. Consider the difference between a restaurant menu and a computer menu. Because of these complexities in mapping metaphors to tasks to user interfaces, Alan Kay prefers the term user illusion , because it is the magic that matters. If a computer did nothing more than to imitate the limitations of the real world, it would be a useless exercise to do anything at all with a computer.