title: Add onKeyDown Event on Varien Data Form Element in Magento
body: <p>I'd like to add event on text element</p>
  
  <pre><code>    $barcodeFieldset = $form-&gt;addFieldset('form_barcode', array('legend' =&gt; Mage::helper('adminhtml')-&gt;__('Barcode Information')));
  
      $barcodeFieldset-&gt;addField('barcode', 'submit', array(
          'label' =&gt; Mage::helper('adminhtml')-&gt;__('Barcode'),
          'name' =&gt; 'barcode',
          'onKeyDown' =&gt; "alert('x')",
          'required' =&gt; true,
          'note' =&gt; 'If You want to scan barcode, focus to this textfield.',
          $this-&gt;_isReadonly() =&gt; $this-&gt;_isReadonly(),
      ));
  </code></pre>
  
  <p>onKeyDown doesn't work. How to make it works?</p>