Active context is a first-class context which combine several ideas found in other programming language abstractions; it shares similarities with environment, contextual layer, module mechanism and persistent object upgrade.
The notion of first-class context is of course borrowed from other work on context-oriented programming. However, unlike other work, the context does not define behavioral variations, but state variations.
The state variations are realized with transformation function, traditionally found in persistent object update mechanism. Objects can then be morphed to adapt to the new shape of the class.
Class name resolution is also contextual. This dynamic binding resembles the notion of environment.
All in all, active context brings modularity, and allow for instance different version of the same class to co-exists.