The document discusses the history and features of PHP Development Tools (PDT). PDT 1.0 was initially contributed by IBM and Zend in 2007, providing PHP capabilities like code assist, debugging, and navigation views. PDT 2.0 utilizes the Dynamic Languages Toolkit to be lighter and faster, with improved memory management and new features like build path configuration, mark occurrences, and type hierarchy. The document provides an example of extending PDT by creating a plugin to warn of potential cross-site scripting vulnerabilities.