/**
  * Renders a list of checkboxes.
  * A checkbox list allows multiple selection, like [[listBox()]].
  * As a result, the corresponding submitted value is an array.
  * The selection of the checkbox list is taken from the value of the model attribute.
  * @param array $items the data item used to generate the checkboxes.
  * The array values are the labels, while the array keys are the corresponding checkbox values.
  * @param array $options options (name => config) for the checkbox list.
  * For the list of available options please refer to the `$options` parameter of [[\yii\helpers\Html::activeCheckboxList()]].
  * @return $this the field object itself
  */
 public function checkboxList($items, $options = [])
 {
     $this->adjustLabelFor($options);
     $this->parts['{input}'] = Html::activeCheckboxList($this->model, $this->attribute, $items, $options);
     return $this;
 }