Application Identifier 253 specifies a Global Document Type Identifier (GDTI). A GDTI is used to identify a document type with an optional serial number.
The GS1 Company Prefix is the first digits of the GDTI, making the number globally unique.
The structure and content of GDTI are determined by the owner of the GS1 Enterprise Prefix and are used to uniquely identify each document type. Ciffed before the optional serial number is a check digit.
The optional serial number is assigned to a single document for the entire life of the document. When the serial number is combined with a GDTI, the whole uniquely identifies each document.
Serial number structure is determined by document owner.