From Xojo Documentation

Displays a class property box for a property that is only available at design time

| name = property's name
| type = type of the property
| owner = the property's owner class
| platform = all/mac/win/linux
| newinversion = version where this class first appeared
| modifiedinversion = version where this class has been modified
| replacementreason = obsolete/deprecated
| replacement = the replacement
Design Property (as Integer)

This ListBox property can only be set in the Inspector and is not available in code.