title: symfony2 customize form select options
body: <p>I'm trying to do a simple form to add an activity with a name and a color.</p>
  
  <p>So I want to make a list with some an array of color, for now it is working I have the name of the color.<br>
  I can add any attribute to my select tag:</p>
  
  <pre><code>$form = $this-&gt;createFormBuilder($myclass)
  -&gt;add('Colors','choice',array('label'=&gt;'select some colors',
              'multiple'=&gt;true,
              'choices'=&gt;array(1=&gt;'red', 2=&gt;'blue', 3=&gt;'green'),
              'attr'=&gt;array('style'=&gt;'width:300px', 'customattr'=&gt;'customdata')
              ));
  </code></pre>
  
  <p>The output will be something like this:</p>
  
  <pre><code>&lt;select name="select" style="width: 300px;" multiple="multiple" customattr="customdata"&gt;
     &lt;option value="1"&gt;red&lt;/option&gt;
     &lt;option value="2"&gt;blue&lt;/option&gt;
     &lt;option value="3"&gt;green&lt;/option&gt;
  &lt;/select&gt; 
  </code></pre>
  
  <p>But how can I add <code>selected="selected"</code> and any attribute I want to my select options ? like this:</p>
  
  <pre><code>&lt;select name="select" style="width: 300px;" multiple="multiple" customattr="customdata"&gt;
     &lt;option style="background-color: #F00;" value="1" selected="selected"&gt;red&lt;/option&gt;
     &lt;option style="background-color: #00F;" value="2" selected="selected"&gt;blue&lt;/option&gt;
     &lt;option style="background-color: #0F0;" value="3"&gt;green&lt;/option&gt;
  &lt;/select&gt; 
  </code></pre>
  
  <p>My question is: how can I add custom attr for <code>option</code> tag (not for <code>select</code> tag) by symfony FormBuilder.<br>
  <strong>NOTICE:</strong> I don't want to use JavaScript. I want to use symfony2 FormBuilder to customize my select options.</p>