span class="string">'-'</span></code> character.
    <code class="code">spec</code> gives the option type and the function to call when this option
    is found on the command line.
    <code class="code">doc</code> is a one-line description of this option.
    <code class="code">anon_fun</code> is called on anonymous arguments.
    The functions in <code class="code">spec</code> and <code class="code">anon_fun</code> are called in the same order
    as their arguments appear on the command line.
<p>

    I