An important attribute of the Drupal development process is the concept that changes need not be backwards compatible with previous major versions. This allows Drupal developers to make changes to the underlying structure of the code making it more robust, easier to maintain, easier to extend, and faster. Sometimes these changes are transparent to site administrators, developers, and themers. In other cases, you may need to make changes to your site, module, or themes to take advantage of this new functionality or make it compatible with the changes.

We will explore these changes in detail in future chapters, but here are some of the major changes that may affect your sites, modules, and themes:

In addition to these changes, several other modifications have been made to Drupal's core functionality, which we will explore throughout the remainder of this book.