Optional [element], Single Occurrence, with Simple Type [inline-Item-Key] localName is [Key] without namespace A list of uniquely keyed items, the key is optional to check that it is required, try to switch to [unique] to test - [key] Instance constraint example from Eleusoft Application Documentation Required [element], Multiple Occurrence, with Complex Type [Item] localName is [Item] without namespace A list of uniquely keyed items, the key is optional to check that it is required, try to switch to [unique] to test - [key] Instance constraint example from Eleusoft Application Documentation