Here I am again...still trying to add a seemingly trivial bit of functionality to xml_iarchive by following the directions at: http://www.boost.org/doc/libs/1_39_0/libs/serialization/doc/derivation.html In my last post (http://lists.boost.org/boost-users/2009/06/49028.php), I was getting several unresolved externals from basic_xml_grammar<char>. I figured I needed to simply explicitly instantiate this template like the others. The first problem with that is that basic_xml_grammar.ipp isn't in boost/archive/impl/ like the other ipp's are. It's in serialization's source directory, which I, like most people, had thrown away after building Boost. So after I copied that file into my own codebase so I could include it and explicitly instantiate basic_xml_grammar<char>, I then got a single unresolved external complaining about basic_xml_grammar<char>::init_chset() not being defined. After some more digging, I found that that particular method is defined in basic_xml_grammar.cpp which is also in serialization's source directory. Even after all that, I'm still getting some other linker errors that nobody here can figure out after hours of trying, but the aforementioned issues alone suggest to me that it isn't currently possible to extend xml_iarchive by following the instructions in the documentation. -Kenny Riddile