Special files
This information is valid for Horde 5 and later only. See <a href="https://wiki.horde.org/Doc/Dev/SpecialFilesH3">Doc/Dev/SpecialFilesH3</a> for Horde 3 or <a href="https://wiki.horde.org/Doc/Dev/SpecialFilesH4">Doc/Dev/SpecialFilesH4</a> for Horde 4.
- horde/lib/core.php: This file
    - sets some required PHP configuration settings
    - sets autoloading paths for Horde libraries
    - registers error handlers
There are several files with a special meaning that can be found in every Horde application:
- index.php: This script is loaded if a user enters an application. Usually this script doesn't have any functionality but simple loads the default view of the application, sometimes depending on the user's preferences.
- lib/Api.php: This files defines and implements all methods that an application is exposing through the <a href="https://wiki.horde.org/Doc/Dev/Registry">Registry</a> to the other Horde applications and the Horde RPC servers.
- lib/Application.php: This file defines information need to initialize the application and to interact with the Horde framework. It also defines the version number of the application.
- lib/Exception.php: This file defines the application-specific exception class.
- lib/Test.php: This file defines any application specific tests to run when using the Horde test script.
- lib/Ajax/Application.php: This file defines the AJAX actions provided by this module.
- themes/default/screen.css: This is a CSS file that defines all application specific style sheet rules.