oad of <code class="computeroutput">+=</code>.</p></li>
<li class="listitem"><p><span class="bold"><strong>Ambiguous return type</strong></span>:
        there is an ambiguity concerning the return value of the
        <code class="computeroutput">+=</code> operation: should it be a reference to the
        signal itself, to enable <code class="computeroutput">sig += slot1 += slot2</code>,
        or should it return a
        <code class="computeroutput"><a class="link" href="../boost/signals2/connection.h