code: public function generateHeader()
      {
          $parts = [];
          $title = $this->owner->generatePanelTitle();
          if ($title) {
              $parts[] = $title;
          }
          $parts[] = Html::beginTag('div', ['class' => 'panel-body']);
  
          return implode("", $parts);
      }
docs: [[@doctodo method_description:generateHeader]].
  
  @return [[@doctodo return_type:generateHeader]] [[@doctodo return_description:generateHeader]]