RWMB_Input_List_Field::normalize PHP Method

    public static function normalize($field)
    {
        $field = $field['multiple'] ? RWMB_Multiple_Values_Field::normalize($field) : $field;
        $field = RWMB_Input_Field::normalize($field);
        $field = parent::normalize($field);
        $field = wp_parse_args($field, array('collapse' => true, 'inline' => null));
        $field['flatten'] = $field['multiple'] ? $field['flatten'] : true;
        $field['inline'] = !$field['multiple'] && !isset($field['inline']) ? true : $field['inline'];
        return $field;
    }

 /**
  * Normalize parameters for field
  *
  * @param array $field
  *
  * @return array
  */
 public static function normalize($field)
 {
     $field = parent::normalize($field);
     $field = wp_parse_args($field, array('flatten' => true, 'query_args' => array(), 'field_type' => 'select_advanced'));
     if ('checkbox_tree' === $field['field_type']) {
         $field['field_type'] = 'checkbox_list';
         $field['flatten'] = false;
     }
     switch ($field['field_type']) {
         case 'checkbox_list':
         case 'radio_list':
             $field['multiple'] = 'radio_list' === $field['field_type'] ? false : true;
             return RWMB_Input_List_Field::normalize($field);
             break;
         case 'select_advanced':
             return RWMB_Select_Advanced_Field::normalize($field);
             break;
         case 'select_tree':
             return RWMB_Select_Tree_Field::normalize($field);
             break;
         case 'select':
         default:
             return RWMB_Select_Field::normalize($field);
             break;
     }
 }