ssage will be queued and will be
posted after the current message has been sent to all the
listeners, and they have all responded.  This is another way in
which posting can be asynchronous; the only sure way to know that
a posting has occurred is through its <cite>callback</cite>. When the posting
is complete, the callback is called, passing it the signal object
that has just completed.</p>
<p>Returns the callback object (or a blank callback object if none
was provided).</p>
<table class="docutils field-lis