H_EXTRA defined, and you must pass the flag
        match_extra to the regex matching functions ( <a class="link" href="regex_match.html" title="regex_match"><code class="computeroutput"><span class="identifier">regex_match</span></code></a>, <a class="link" href="regex_search.html" title="regex_search"><code class="computeroutput"><span class="identifier">regex_search</span></code></a>, <a class="link" href="regex_iterator.html" title="regex_iterator"><code class="computeroutput"><span class="identifier">r