"special">(),</span>
    <span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span> <span class="special">&gt;&gt;</span> <span class="identifier">x3</span><span class="special">::</span><span class="identifier">double_</span><span class="special">,</span>       <span class="comment">// parser grammar</span>
    <span class="identifier">x3</span><span class="special">::</span><span class="identifier">space</span><span class="special">,</span>                    