Robert Brodt Messages: 802 Registered: August 2010 Location: Colorado Springs, CO
Page 17 of the spec talks about conventions used in the document. The cardinality operators mentioned there apply to UML diagrams that describe the BPMN2 model, not to the elements of the model itself.
BPMN2 only allows you to specify whether or not a Data Type (a.k.a. "ItemDefinition") is a collection or not. It does not allow you to put constraints on the number of items that collection may (or must) contain.