title: Yii 2 GridView - set options for filter input field(s)
body: <p>As I've read the documents and tried everything, there's no way to add an <code>input-sm</code> HTML/Bootstrap class to the filter input fields of the <code>GridView</code> widget in Yii 2.</p>
  
  <p>One thing I can do is to use <code>jQuery</code>, search for those elements and add them an <code>input-sm</code> class.</p>
  
  <p>Is there a way to achive this in Yii 2?</p>