title: ExtJs dependent field validation
body: <p>How do I validate one field which is dependent on another field?</p>
  
  <pre><code>{
    xtype:          'textfield',
    name:           'name2',
    vtype:          'type',      // how to write the validation code for this if it 
                                 // depends on the value of another field?
    allowBlank:     false
  }
  </code></pre>