A number which specifies the ordinal position of the product in a collection. The ordinal position may be a simple number (1st, 2nd, 3rd etc) or may be multi-level (eg 3.2) if the collection has a multi-level structure (ie there are both collection and sub-collection title elements). Mandatory and non-repeating within the <CollectionSequence> composite.

New from 3.0.4 A hyphen may be used in place of an integer within a multi-level number, where a particular level of the hierarchy is unnumbered, for example -.3 where a product is the third in a sub-collection, and the sub-collections are in no particular order within the collection.