...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
boost::xpressive::operator<< — insertion operator for sending sub-matches to ostreams
template<typename BidiIter, typename Char, typename Traits> std::basic_ostream< Char, Traits > & operator<<(std::basic_ostream< Char, Traits > & sout, sub_match< BidiIter > const & sub);