J rn Zaefferer is a professional software developer from Cologne, Germany. He creates application programming interfaces (APIs), graphical user interfaces (GUIs), software architectures, and designs databases, for both web and desktop applications. His work focuses on the Java-platform, while clientside-scripting evolves around jQuery. He started contributing to jQuery in mid-2006, and has since co-created and maintained QUnit, jQuery’s unit testing framework; released and maintained a half-dozen of very popular jQuery plugins, and contributed to jQuery books as both author and tech-reviewer. He also is a lead developer for jQuery UI.