title: Yii2 Date compare validation
body: <p>I have model rules() like below, but it is not working. It is showing error message always.</p>
  
  <pre><code>public function rules()
  {
      return [
          [['start_date','end_date'], 'date', 'format' =&gt; 'php:F d Y'],
          ['start_date','compare','compareAttribute'=&gt;'end_date','operator'=&gt;'&lt;'],
          ['end_date','compare','compareAttribute'=&gt;'start_date','operator'=&gt;'&gt;'],
      ];
  }
  </code></pre>