[Boost-users] [serialization] Best way to serialize to an old file version

What is the best way to write archives to an old version? Say I have version 23 of our product and want to write an archive that another user with version 22 can read. The serialization keeps track of the version on a class level. But in this use case I need to know the version of each class at a specific point in time. Sure, I could implement some global variable and completely work around the version system of boost serialization. But I hope there is a better, preferred way. Rgds Richard