dex contained within submatches vector; if <code class="computeroutput"><span class="identifier">submatches</span><span class="special">[</span><span class="number">0</span><span class="special">]</span></code>
        is -1, then the first string enumerated for each match will be all of the
        text from end of the last match to the start of the current match, in addition
        there will be one extra string enumerated when no more matches can be found:
        from the end of the last match found, t