>
    <span class="identifier">traits</span><span class="special">::</span><span class="identifier">push_back</span><span class="special">(</span><span class="identifier">attr</span><span class="special">,</span> <span class="identifier">val</span><span class="special">);</span>
    <span class="identifier">traits</span><span class="special">::</span><span class="identifier">clear</span><span class="special">(</span><span class="identifier">val</span><span class="special">);</span>
<span class="special">}</