Hi Robert, Once again I find myself confounded by the true concept requirements for archives. Once upon a time, the truth-as-we-knew-it was that the following (copied from the library docs) was part of the input archive requirements. All input archives should be derived from the following template: template<class Archive> detail::common_iarchive; But, as I just discovered: polymorphic_iarchive doesn't meet those requirements. Since you have struggled with how to write the concept requirements for archives, I have a brilliant suggestion: create concept checking classes and archetypes using Boost.ConceptCheck, and use those to formulate and validate your concepts. Then you can simply copy the concept checking classes into your documentation and add a description of semantic constraints. You can't go wrong if you do that; the compiler will check your work for you, and make sure your code is consistent with your documentation. [I have recently upgraded the ConceptCheck library to allow some nicer but as-yet-undocumented syntax. When (if?) you decide to do this, I'll give you the quick skinny] -- Dave Abrahams Boost Consulting www.boost-consulting.com