Description could be found in doc files distributed with Beta1. ILinstrset.doc, IL Programmers Reference etc. It seems that OptIL/annotations idea was dropped. This paper: http://www2.fit.qut.edu.au/CompSci/PLAS/ComponentPascal/VirtualMachines.ps has some (limited) info on this. This document should be also useful to you if you're comparing Java bytecodes and CIL. Sergey