</tr>
<tr><td align="left" valign="top"><p>
              <code class="computeroutput"><span class="identifier">T</span></code> is required to be
              a container type. If <a class="link" href="../../../advanced/customize/is_container.html" title="Determine if a Type Should be Treated as a Container (Qi and Karma)"><code class="computeroutput"><span class="identifier">traits</span><span class="special">::</span><span class="identifier">is_container</span></code></a> does not return
              tr