he type of <code class="computeroutput"><span class="identifier">a</span></code> or
                  if it is a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy
                  Argument</a>, its return type.
                </p></dd>
</dl>
</div>
<h6>
<a name="spirit.qi.reference.auxiliary.attr.h4"></a>
            <span class="phrase"><a name="spirit.qi.reference.auxiliary.attr.expression_semantics"></a></span><a class="link" href="attr.html#spirit.qi.reference.auxilia