title: Logic for Symfony form filter field with more than one element
body: <p>I am implementing a <strong>negation</strong> filter field in Symfony 1.4. with 1 text input and 1 checkbox for negation.</p>
  
  <p>I can access the input value as below</p>
  
  <pre><code>public function addXXXColumnQuery($query, $field, $value)
  {
      $v = $value['text'];
      $n = 'negation_checkbox_true_or_false'; // don't know how?
  
      if ($n === true) 
      {
          $query-&gt;addWhere($query-&gt;getRootAlias().'.name = ?', $v);
      } 
      else if ($n === false) 
      {
          $query-&gt;addWhere($query-&gt;getRootAlias().'.name &lt;&gt; ?', $v);
      }
  }
  </code></pre>
  
  <p>but I can't figure out how to access the checkbox value.</p>
  
  <p><strong>sfWidgetFormInputFileEditable</strong> has a 'with_delete' option that prints a checkbox. Anyone knows where is the code that checks for that value and delete the file?</p>
  
  <p>If I can find that, maybe I can figure that out.</p>