HKAU
This variable is the alias for the HKEY_ALL_USERS registry root and is used to abbreviate the registry hive name HKEY_ALL_USERS in registry paths.
Note: HKEY_ALL_USERS is used by InstallMate to refer to the registry root that is mapped to either HKEY_CURRENT_USER or HKEY_LOCAL_MACHINE, depending on the installation mode (Current User or All Users, respectively).
Usage
Used internally by InstallMate. You can refer to this variable as <HKAU>. It is normally used as part of a registry path, as in <@<HKAU>\...remainder of path...>. This variable is read-only; do not try to change it.