Drupal 6 Theme Registry

Drupal's theme registry maintains cached data on the available theming hooks and how to handle them.

For most theme developers, the registry does not have to be dealt with directly. Just remember to clear it when adding or removing theme functions and templates. Editing existing functions and templates does not require a registry rebuild.

To clear the theme registry, do one of the following things:

1. On the "Administer > Site configuration > Performance" page, click on the "Clear cached data" button.
2. With devel block enabled (comes with devel module), click the "Empty cache" link.
3. The API function drupal_rebuild_theme_registry.

The theme registry is cached data instructing Drupal on the available theming hooks and how to handle it by indicating its type. In previous versions all theming calls were handled on the fly. Since a lot more work is being done under the hood, the cached instructions speeds up the process especially for templates. The theme engine your theme is running under should automatically register all the theming hooks for you.

There are special cases where you may need to work with the registry directly. When your theme requires a new hook to be registered that was not already implemented on the layers below it (core, modules, engine). This includes some forms when they are not explicitly themed by core or modules but instead rely on the default form presentation.

* More details can be found in the sub-page, The theme registry for special cases.
* Do not confuse the theme registry with the theme's .info file which is also cached. Points 1 and 2 on clearing the registry will clear both.
* Your theme must be using phptemplate engine for the for its templates and functions to be discovered. Other engines should behave the same way. For engineless themes, it must be done manually. See phptemplate_theme to see how it is done.