code: public function canCaptureBlock($block)
      {
          $blockClass = get_class($block);
  
          if (!$this->canCaptureCoreBlocks() && strpos($blockClass, 'Mage_') === 0) {
              return false;
          }
  
          // Don't capture debug blocks
          if (strpos($blockClass, 'Sheep_Debug_Block') > 0) {
              return false;
          }
  
          return true;
      }
docs: Logic that checks if we should capture specified block
  
  @param $block Mage_Core_Block_Abstract
  @return bool