lass="identifier">what_</span><span class="special">;</span>       <span class="comment">// Information about the nature of the error.</span>
<span class="special">};</span>
</pre>
<h6>
<a name="spirit.qi.reference.directive.expect.h4"></a>
            <span class="phrase"><a name="spirit.qi.reference.directive.expect.expression_semantics"></a></span><a class="link" href="expect.html#spirit.qi.reference.directive.expect.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
         