When this parameter is enabled/ON and a KEY= option is provided on a KEN or KEP function, the system will NOT require that a record with the key specified exist, and will merely use the key specified for file positioning.

When the parameter is disabled/OFF an error will be generated if there is no record with the key specified.

In addition, when this parameter is enabled and using the KEN function against an alternate key that allows duplicates, the KEN function will return the next higher logical key.

For example, based on a file with the following values:

Given the above information, the secondary keys consist of 5 records with CAT followed by 3 records with DOG.

If you had the '+K' parameter enabled, thus using the advanced functionality, a KEN(file, KEY="CAT", KNO=1) will return "DOG", but with '+K' disabled it will return CAT. The advanced KEN functionality will always return you the next valid higher key on the file rather than just the key of the next record on the file.