title: zend-form select optgroup, how to specify id
body: <p>Hello i am using <em>Zend Framework Form</em> and have tried to get this example to work <a href="http://framework.zend.com/issues/browse/ZF-8252" rel="nofollow">http://framework.zend.com/issues/browse/ZF-8252</a>, but it fails xD</p>
  
  <p>this is my code</p>
  
  <pre><code>$options = Array
  (
      [] =&gt; Qualsiasi Agente
      [agenti_attivi] =&gt; Array
          (
              [4] =&gt; Giovanni Abc
              [10] =&gt; Luigi Abc
              [13] =&gt; Michela Abc
          )
  
  );
  
  $agenti-&gt;addMultiOptions($options);
  </code></pre>
  
  <p>and the generated code is :</p>
  
  <pre><code>&lt;select name="agente_id" id="agente_id" tabindex="6"&gt;
      &lt;option value="" label="Qualsiasi Agente" selected="selected"&gt;Qualsiasi Agente&lt;/option&gt;
      &lt;optgroup id="agente_id-optgroup-Agenti attivi: " label="Agenti attivi: "&gt;
      &lt;option value="4" label="Giovanni Abc"&gt;Giovanni Abc&lt;/option&gt;
      &lt;option value="10" label="Luigi Capoarea"&gt;Luigi Abc&lt;/option&gt;
      &lt;option value="13" label="Michela Abc"&gt;Michela Abc&lt;/option&gt;
      &lt;/optgroup&gt;
  
  &lt;/select&gt;
  </code></pre>
  
  <p>where <strong>id="agente_id-optgroup-Agenti attivi: "</strong>  is not xhtml valid <em>Line 724, Column 44: value of attribute "id" must be a single token</em></p>
  
  <p>i am using zend 1.11.10</p>
  
  <p>thanks</p>