 class="code"><span class="constructor">Arg</span>.current</code>.  You must set
  it before calling <code class="code">parse_argv</code>.  The initial value of <code class="code">current</code>
  is the index of the program name (argument 0) in the array.
  If an error occurs, <code class="code"><span class="constructor">Arg</span>.parse_argv</code> raises <code class="code"><span class="constructor">Arg</span>.<span class="constructor">Bad</span></code> with
  the error message as argument.  If option <co