an></code>
          class. The output operator is still used by formatters and not required
          by the filter factory. Now we can define and register the filter factory:
        </p>
<p>
</p>
<pre class="programlisting"><span class="comment">// Custom point filter factory</span>
<span class="keyword">class</span> <span class="identifier">point_filter_factory</span> <span class="special">:</span>
    <span class="keyword">public</span> <span class="identifier">logging</span><span class="special">::</s