This information is valid for Horde 3 only. See Doc/Dev/SpecialFilesH4 for Horde 4 or Doc/Dev/SpecialFiles for Horde 5 and later.
horde/lib/core.php: This file
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/base.php: This file is loaded from every script of the application. Its purpose is to:
core.phplib/api.php: This files defines and implements all methods that an application is exposing through the Registry to the other Horde applications and the Horde RPC servers.lib/version.php: This files defines a single constant: the application's version number.templates/common-header.inc: This is the common page header template for all scripts of the application. All applications use the same page footer template horde/templates/common-footer.inc.themes/screen.css: This is a CSS file that defines all application specific style sheet rules.