erence.directive.omit.h4"></a>
            <span class="phrase"><a name="spirit.qi.reference.directive.omit.expression_semantics"></a></span><a class="link" href="omit.html#spirit.qi.reference.directive.omit.expression_semantics">Expression
            Semantics</a>
          </h6>
<p>
            Semantics of an expression is defined only where it differs from, or
            is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span 