Clearing the theme registry

Before we begin, we need to familiarize ourselves with a seemingly trivial yet crucial task that needs to be performed on a routine basis during theme development clearing the theme registry. The theme registry is essentially a table that Drupal uses to list and track the files and features of a theme as well as the theme functions which are being exposed by modules and the theme itself.

While it is a recommended practice to turn on Drupal's cache feature only for production sites, the theme registry is built and cached regardless of other caching options. As a result, any changes that affect the structure of the theme will necessitate the clearing of the theme registry.