[boost] Boost API System or Library Calls ..

Out of curiosity, wish to know if BOOST ASIO calls like - boost::asio::read() boost::asio::transfer_all() boost::asio::write() BOOST LEXICAL calls like - boost::lexical_caststd::string() BOOST POSIX TIME calls like - boost::posix_time::microsec_clock::universal_time() boost::posix_time::microsec_clock::ptime() are LIBRARY or SYSTEM calls. How to know which calls of BOOST are SYSTEM and LIBRARY calls? Thanks.