[boost] Deciding what to put in `namespace detail`

For my future Boost.RDB submission, I feel tempted to put everything except the names that are in the public (documented) interface in a nested `namespace detail`. Why not even put *everything* there and copy selected names in the public namespace by means of using-declarations. Has it been already done ? And what about having three namespaces : a "public" one for the user, a "protected" one for those extending the lib, and a "private" one for undocumented internals? Opinions and advise welcome... J-L