Use the HIDDEN-DATA special property to store data that you want to permanently hide from the user. For example, if you need to store a composite key to simplify finding a corresponding record in a file, store the key in HIDDEN-DATA.
For data that you want to hide from the user intermittently, use the PHYSICAL-COLUMNS special property to hide and reveal the data as required. Do not use this method to store data that you do not want to reveal to the user at any time.