Placholder for TbExtendedGridView search input

Question

I'm using TbExtendedGridView within the Yii framework with Bootstrap extension to display data in a tabular format. I have a search field within this interface, but I'd like to add a placeholder to assist users in navigating this field.

Below is a snippet of my code responsible for initializing and configuring this grid:

$this->widget('bootstrap.widgets.TbExtendedGridView', array(
  'id' => 'xtag-grid',
  'responsiveTable' => true,
  'dataProvider' => $model->search(),
  'type' => 'bordered striped',
  'filter' => $model,
  'columns' => array(
    // Column definitions...
  ),
));

How can I add a placeholder to the search field displayed in the grid's filter using this code?

I tried to add htmlOptions => array('placeholder' => 'My placeholder'), but the placeholder was added to the div element that wraps the table.

Thank you for your assistance.