identifier">Traits</span><span class="special">,</span> <span class="identifier">Compare</span><span class="special">,</span> <span class="identifier">Combine</span><span class="special">,</span> <span class="identifier">Section</span><span class="special">,</span> <span class="identifier">Alloc</span> <span class="special">&gt;</span><span class="special">&gt;</span> <span class="special">{</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <span class="identifier">has_in