Indeed, the "valid but unspecified state" refers only to some types defined in the he standard library. It essentially means that you can only call methods which have no preconditions and don't depend on what that state is, e.g. assignment or destruction, or something like string::clear or vstring::assign if you want defined outcomes. In general each type is free to guarantee whatever the author wants about the moved from state, e.g. moved-from std::unique_ptr is always null.