BlockManager::getUseExtraCSSClasses PHP Method

    public function getUseExtraCSSClasses()
    {
        $config = $this->getThemeConfig();
        return isset($config['use_extra_css_classes']) ? $config['use_extra_css_classes'] : false;
    }

 /**
  * CSS Classes to apply to block element in template
  * @return string $classes
  */
 public function CSSClasses($stopAtClass = 'DataObject')
 {
     $classes = strtolower(parent::CSSClasses($stopAtClass));
     if ($this->blockManager->getUseExtraCSSClasses()) {
         $classes = $this->ExtraCSSClasses ? $classes . " {$this->ExtraCSSClasses}" : $classes;
     }
     return $classes;
 }