Hello, I saw the following thread talking about how to set regex to work in perl extended mode: http://groups.google.com/group/boost-list/browse_thread/thread/4d5588fb70211e02/2c4a6026becb9bd4?lnk=st&q=&rnum=2#2c4a6026becb9bd4 I am using 1.28.0 and has coded something like this already: boost::RegEx expr(is10k ? keywords_10k[i].m_Key : keywords_10q[i].m_Key, true); // Pass callback, strings to RegEx library unsigned int result = expr.Grep(cb, pBuf); question is how do I set this boost::regex_constants::perl like the follow example: boost::regex rxBlah("([a-z](?:_?[a-z0-9])*)_dvs", boost::regex_constants::perl | boost::regex_constants::icase); /Winson