  Studies of Aspect-Oriented Programming (AOP) usually focus on a language in
which a specific aspect extension is integrated with a base language. Languages
specified in this manner have a fixed, non-extensible AOP functionality. In
this paper we consider the more general case of integrating a base language
with a set of domain specific third-party aspect extensions for that language.
We present a general mixin-based method for implementing aspect extensions in
such a way that multiple, independently developed, dynamic aspect extensions
can be subject to third-party composition and work collaboratively.
