code: public function generateStart()
      {
          $parts = [];
          foreach ($this->owner->widgetClasses as $class) {
              Html::addCssClass($this->owner->htmlOptions, $class);
          }
          $parts[] = Html::beginTag('div', $this->owner->htmlOptions);
  
          return implode("", $parts);
      }
docs: [[@doctodo method_description:generateStart]].
  
  @return [[@doctodo return_type:generateStart]] [[@doctodo return_description:generateStart]]