handler_result</span><span class="special">::</span><span class="identifier">fail</span><span class="special">;</span>
    <span class="special">}</span>
<span class="special">};</span>
</pre>
<p>
        <code class="computeroutput"><span class="identifier">x3</span><span class="special">::</span><span class="identifier">error_handler_tag</span></code> is a special tag we will
        use to get a reference to the actual x3::error_handler that we will inject
        at very start, when we call parse. We ge