title: How to add class to form-group div of ActiveField in YII2?
body: <p>I have some code below:</p>
  
  <pre><code>&lt;?=
    $form-&gt;field($model, 'phone_no')-&gt;textInput(
      [
        'placeholder' =&gt;
        '(Conditionally validated based on checkbox above, groovy!)'
      ]
    )
  ?&gt;
  </code></pre>
  
  <p>Which results in HTML:</p>
  
  <pre><code>&lt;div class="form-group field-contactform-phone_no"&gt;
    &lt;label class="control-label"&gt;Phone No
    &lt;input type="text" aria-describedby="hint-contactform-phone_no" placeholder="(Conditionally validated based on checkbox above, groovy!)" name="ContactForm[phone_no]" id="contactform-phone_no" class=""&gt;&lt;/label&gt;
    &lt;small class="error-box"&gt;&lt;/small&gt;
    &lt;p class="help-text" id="hint-contactform-phone_no"&gt;&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>My Question is:</p>
  
  <p>How can I add a class 'invisible' to the outer div (containing class=form-group currently)?</p>
  
  <p>Thanks for help </p>