How MUD's work >
Extensibility is one of the most powerful features of MUD's. MUD worlds and characters are dynamically extensible -- they can gain or lose objects, magical powers, and intellectual and physical attributes at any time. For example, a room might gain a new door, a world a new forest, or a character the ability of flight. From a conceptual perspective there are few barriers to the development of person and place in a MUD aside from the human imagination.
Interestingly, the very first MUD environment was dynamically configurable by users. Trubshaw and Bartle provided a power user level called a Wizard in their original MUD. Although the feature had originally been included simply as a debugging tool intended to be used just for development, it's potential became apparent as an intrinsic part of the game.
Later MUD's also provided users with the ability to change the worlds they found themselves in, adding spaces, objects, characters, and capabilities. Some sophisticated MUD's even include a built-in programming language and object oriented properties like inheritance to enable very powerful additions and changes.
Extensible MUD's take the concept of a virtual world -- already a powerful intellectual concept -- one step farther, giving visitors to that world the ability to change it in real-time. One might wonder at what point the complexity of these worlds will evolve to the point that they become sentient...