n class="identifier">boost</span> <span class="special">{</span>
  <span class="keyword">namespace</span> <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">namespace</span> <span class="identifier">traits</span> <span class="special">{</span>
        <span class="keyword">typedef</span> <span class="emphasis"><em><span class="identifier">unspecifie