code: public function core_block_abstract_to_html_after(Varien_Event_Observer $params) {
  
          if (!$this->showHints()) {
              return;
          }
  
          if (substr(trim($params->getTransport()->getHtml()), 0, 4) == 'http') {
              return;
          }
  
          $wrappedHtml = '';
  
          $block = $params->getBlock(); /* @var $block Mage_Core_Block_Abstract */
  
          // will only be called once and allows renderes to initialize themselves (e.g. adding js/css)
          if ($this->init && $this->afterHead && !Mage::getStoreConfigFlag('advanced/modules_disable_output/' . $block->getModuleName()) && $block->getNameInLayout()) {
              $wrappedHtml = '<!-- INIT AOE_TEMPLATEHINTS RENDERER START -->' . $this->getRenderer()->init($wrappedHtml) . '<!-- INIT AOE_TEMPLATEHINTS RENDERER STOP -->';
              $this->init = false;
          }
  
          if ($block->getNameInLayout() == 'head') {
              $this->afterHead = true;
          }
  
          $transport = $params->getTransport();
  
          $this->hintId++;
  
          $wrappedHtml .= $this->getRenderer()->render($block, $transport->getHtml(), $this->hintId);
  
          $transport->setHtml($wrappedHtml);
      }
docs: Event core_block_abstract_to_html_after
  
  @param Varien_Event_Observer $params
  @return void
  @author Fabrizio Branca
  @since 2011-01-24