/em></span></a>
      evolved over years in a fairly complex directory structure:
    </p>
<pre class="programlisting"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">actor</span>
<span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">attribute</span>
<span class="identifier">boost</span><span 