<span class="identifier">histogram</span> <span class="special">{</span>
    <span class="keyword">namespace</span> <span class="identifier">axis</span> <span class="special">{</span>
      <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Value<span class="special">,</span> <span class="keyword">typename</span> MetaData<span class="special">,</span> <span class="keyword">typename</span> Options<span class="special">,</span> 
               <span cla