e to be added to the
   <code>W3CEndpointReference</code></dd>
<dd><code>value</code> - extension attribute value</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>A <code>W3CEndpointReferenceBuilder</code> instance with
   the extension attribute added to the <code>W3CEndpointReference</code>
   instance.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/IllegalArgumentException.html?is-external=true" title="class or inte