Computational reflection is gaining interest in practical applications as witnessed by the use of reflection in the Java programming environment and recent work on reflective middleware. Reflective systems offer many different reflection programming interfaces, the so-called Meta-Object Protocols (MOPs). Their design is subject to a number of constraints relating to, among others, expressive power, efficiency and security properties. Since these constraints are different from one application to another, we should be able to easily provide specially-tailored MOPs