app/code/community/Aoe/TemplateHints/Model/Observer.php
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);
    }
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);
    }
Event core_block_abstract_to_html_after

@param Varien_Event_Observer $params
@return void
@author Fabrizio Branca
@since 2011-01-24