Horde applications work with a standard set of constants:

• HORDE_BASE: The filesystem location of Horde (defined in each application).
• APP_BASE: The filesystem location of the application.
• APP_NAME: The name to use for the application.
• APP_VERSION: The version number of the application (not a CVS revision tag).

Applications also define constants for all of the actions that they perform through form submission. Class libraries define constants for arguments and return values.