de class="code">-help</code> or <code class="code">--help</code> is
  given, <code class="code"><span class="constructor">Arg</span>.parse_argv</code> raises <code class="code"><span class="constructor">Arg</span>.<span class="constructor">Help</span></code> with the help message
  as argument.<br>
</div>
<pre><span id="EXCEPTIONHelp"><span class="keyword">exception</span> Help</span> <span class="keyword">of</span> <code class="type">string</code></pre>
<div class="info">
Raised by <code class="code"><span