title: Yii 2 Field 2 must have greater value than Field 1
body: <p>I've just started with Yii (2.0) and I have a problem.</p>
  
  <p>I need to make sure that the Maximum Order Quantity is always equal or greater than the Minimum Order Quantity. Which means, that you can't order a minimum of 10, and maximum of 5 for example.</p>
  
  <p>Here is a screenshot. </p>
  
  <p><img src="https://i.stack.imgur.com/HQWq4.png" alt="enter image description here"></p>
  
  <p>And some code:</p>
  
  <pre><code>    &lt;?= $form-&gt;field($model, 'minimum_order_quantity')-&gt;widget(TouchSpin::classname(), [
      'options' =&gt; [
          'placeholder' =&gt; 'Minimum Order Quantity ...',
          'class' =&gt; 'input-lg',
      ],
      'pluginOptions' =&gt; [
          'buttonup_class' =&gt; 'btn btn-primary', 
          'buttondown_class' =&gt; 'btn btn-info', 
          'buttonup_txt' =&gt; '&lt;i class="glyphicon glyphicon-plus-sign"&gt;&lt;/i&gt;', 
          'buttondown_txt' =&gt; '&lt;i class="glyphicon glyphicon-minus-sign"&gt;&lt;/i&gt;'
      ],
  ]) ?&gt;
  
  &lt;?= $form-&gt;field($model, 'maximum_order_quantity')-&gt;widget(TouchSpin::classname(), [
      'options' =&gt; [
          'placeholder' =&gt; 'Maximum Order Quantity ...',
          'class' =&gt; 'input-lg',
      ],
      'pluginOptions' =&gt; [
          'buttonup_class' =&gt; 'btn btn-primary', 
          'buttondown_class' =&gt; 'btn btn-info', 
          'buttonup_txt' =&gt; '&lt;i class="glyphicon glyphicon-plus-sign"&gt;&lt;/i&gt;', 
          'buttondown_txt' =&gt; '&lt;i class="glyphicon glyphicon-minus-sign"&gt;&lt;/i&gt;'
      ],
  ]) ?&gt;
  </code></pre>
  
  <p>This would be the _form.php.</p>
  
  <p>Thanks in advance!</p>