title: Add prefix and remove space for 'option' in 'optgroup'
body: <pre><code>&lt;select&gt;
    &lt;optgroup label="Swedish Cars"&gt;
      &lt;option value="volvo"&gt;Volvo&lt;/option&gt;
      &lt;option value="saab"&gt;Saab&lt;/option&gt;
    &lt;/optgroup&gt;
    &lt;optgroup label="German Cars"&gt;
      &lt;option value="mercedes"&gt;Mercedes&lt;/option&gt;
      &lt;option value="audi"&gt;Audi&lt;/option&gt;
    &lt;/optgroup&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>This returns:</p>
  
  <pre class="lang-none prettyprint-override"><code>Swedish Cars
    Volvo
    Saab
  German Cars
    Mercedes
    Audi
  </code></pre>
  
  <p>This is ok, but I would like to add before Volvo, Saab, Mercedes and Audi own prefix, for example ">" and remove empty space like this:</p>
  
  <pre class="lang-none prettyprint-override"><code> Swedish Cars
   &gt;Volvo
   &gt;Saab 
   German Cars
   &gt;Mercedes
   &gt;Audi
  </code></pre>
  
  <p>Is this possible? If yes, how?</p>