"Web 2.0 applications and sites commonly employ a number of technologies: PHP, MySQL, XHTML, CSS, JavaScript/Ajax, microformats (standard formats for HTML data), tags (keywords for categorizing site content), and Web feeds (formatted and streamed Web content, usually in XML, such as an RSS feed). Because learning and using most of these technologies can be rather challenging to a Web developer, perhaps the best way to get started doing so is by using all of them to create a single Web-based application, with no pretense at mastering any one of them. This is the approach taken in Quentin Zervaas's book, Practical Web 2.0 Applications with PHP."