Hi, Here some implementation questions I've got: 1. Why does the library brake const correctness. FWIV I could write: const vector<int>& v = ...; std::cin >> io::formatob( v ); and it would compile without questions. 2. Why doesn't insert_iterator is implemented using iterator_facade? 3. Why do you need 2 different functions containerfmtex and containerfmt? 4. How does this all machinery will work with wchar_t? 5. Why do you need static_cast< const base_type * > to cast to the base type in container.hpp? 6. Why the same entity you sometime call format_type and sometime DelimeterType? 7. What deducer is supposed to deduce? I couldn't get through all the details, but couldn't the same be achieved using partial specialization and/or partial ordering. Cause it look way too complex and unnecessary. 8. Why class formatter, formatter_t is defined in namespace io, while it reside among details headers? 9. What is RT2 stands for? 10. detail/formatter.hpp refer to openclose_formatter_t, but does not include no headers. 11. Need for all this hierarchies: Formatter->formater_t->openclose_formatter_t openclose_formatter->openclose_formatter_t are completely unclear. Explanations presented in docs does not help since format methods seems to be returning *this anyway. Why couldn't we just use something trivial like template<char Ch> struct formatter { std::basic_string<Ch> m_open; std::basic_string<Ch> m_close; std::basic_string<Ch> m_sep; }; Is beyond me. If any member is empty it means it missing. 12. select and switch templates seems useful. Why doesn't MPL provide these? 13. Doesn't MPL provide eq_int, lt_int? 13. struct selector needs to be PP generated 14. list_object -> formatter_t inheritance look wrong. Where is IS A relationship? 15. You couldn't do this: typename InputStream::char_type ch = '\0'; I think It all for now. Please comment. Gennadiy.