al attribute of for the
          subject:
        </p>
<p>
</p>
<pre class="programlisting"><span class="keyword">typename</span> <span class="identifier">traits</span><span class="special">::</span><span class="identifier">attribute_of</span><span class="special">&lt;</span><span class="identifier">Subject</span><span class="special">,</span> <span class="identifier">Context</span><span class="special">&gt;::</span><span class="identifier">type</span> <span class="identifier">val</span><span class="specia