>  <span class="comment">// All options off. </span>
        <span class="keyword">typedef</span> <a class="link" href="../boost/histogram/axis/option/bit.html" title="Struct template bit">bit</a><span class="special">&lt;</span> <span class="number">0</span> <span class="special">&gt;</span> <a name="boost.histogram.axis.option.underflow_t"></a><span class="identifier">underflow_t</span><span class="special">;</span>  <span class="comment">// Axis has an underflow bin. Mutually exclusive with <code class="