[Boost-users] boost serialisation 1.56, why does library version change, when no change in library ?

At boost 1.53 the library version was 10, however at boost 1.56 it has jumped to 11. I have not seen any documentation/release notes about boost serialisation changes. What has changed in boost serialisation to merit this change ? The documentation in $BOOST_ROOT/libs/serialization/basic_archive.cpp describes the changes to boost library version, however it does *not* describe why it jumped from 10 -> 11. Any help appreciated. Ta, Avi