PropertyHandle :: IsUniqueCollection - Is collection unique collection
A collection is unique, when it ensures, that it may not contain duplicate instances, i.e. instances with the same identity. A collection is considered as unique, when it has at least one unique index (sort order) or when dimension is 1. Arrays are never considered as unique collections.
Return value: Return value ( logical )
The function returns YES when the question was answered positively. Otherwise it returns NO.