r</span><span class="special">::</span><span class="identifier">attr</span><span class="special">&lt;</span> <span class="identifier">severity_level</span> <span class="special">&gt;(</span><span class="string">"Severity"</span><span class="special">)</span> <span class="special">&gt;=</span> <span class="identifier">warning</span><span class="special">);</span>
    <span class="identifier">sink</span><span class="special">-&gt;</span><span class="identifier">set_formatter</span>
    <span class="special">(