Apache is a free and open-source cross-platform web server software.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
PHP is a general-purpose scripting language used for web development.
Priority Hints exposes a mechanism for developers to signal a relative priority for browsers to consider when fetching resources.
YUI is a JavaScript and CSS library with more than 30 unique components including low-level DOM utilities and high-level user-interface widgets.