use this tag to send or receive messages, it may be useful when monitoring communication patterns.</p>
<p>
</p>
<div class="variablelist"><table border="0">
<col align="left" valign="top">
<tbody><tr>
<td><p><span class="term">Returns:</span></p></td>
<td><p>the tag value used for collective operations. </p></td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">static</span> <span class="identifier">optional</span><span class="special">&lt;</span> <sp