@REGEXIST[HKEY...\key] : Returns 1 if the specified key exists, 0 otherwise
The expression must be enclosed in double quotes if it contains any separator characters (space, comma, or tab).
If you are running a 64-bit version of Windows, you can access the 64-bit registry instead of the 32-bit registry by appending "_64" to the HKEY name.
If the key name begins with \\machinename, @REGEXIST opens the registry on a remote machine. The remote registry service must be running on the remote machine, and you must have access and permissions. The HKEY parameter can be one of the following keys:
HKEY_CLASSES_ROOT (or HKCR)
HKEY_CURRENT_CONFIG (or HKCC)
HKEY_CURRENT_USER (or HKCU)
HKEY_LOCAL_MACHINE (or HKLM)
HKEY_PERFORMANCE_DATA (or HKPD)
HKEY_USERS (or HKU)
See @REGCREATE for information on the format of the key name.