Property :: autoNumber - Get value for auto-number

When defining an auto-number attribute __AUTOIDENT for an instances and providing an index for this attribute (sort order), the auto-number will be set automatically, when creating new instances in the collection.

The function returns the next value for the auto-number for the property. The auto-number is evaluated for the topmost superset (not for the current collection, when is is based on a superset). One one may call the function in order to set the next auto-number in an initialized instance or using is as new key value when duplicating (copying) an instance within a collection.

When the complex data type for the property does not contain an __AUTOIDENT attribute, the function throws an exception. The function also throws an exception, when no instance is selected or when a 0 -value could not be updated because the instance is read only.