<simpleType name="ReferenceType">
    <annotation>
        <documentation>Identifies what kind of document is being referenced.</documentation>
    </annotation>
    <restriction base="NMTOKEN">
        <enumeration value="AppointmentNumber" />
        <enumeration value="Authorization" />
        <enumeration value="BookingNumber" />
        <enumeration value="ContractNumber" />
        <enumeration value="CustomerMasterRecordNumber" />
        <enumeration value="CustomerOrderNumber" />
        <enumeration value="DeliveryNote" />
        <enumeration value="LineItemNumber" />
        <enumeration value="LetterOfCredit" />
        <enumeration value="LoadPlanningNumber" />
        <enumeration value="PickUpNumber" />
        <enumeration value="PRONumber" />
        <enumeration value="PurchaseOrderNumber" />
        <enumeration value="RequestForQuoteNumber" />
        <enumeration value="RequisitionNumber" />
        <enumeration value="SalesOrderReference" />
        <enumeration value="ShipmentIdentifier" />
        <enumeration value="Other" />
    </restriction>
</simpleType>

• ReferenceType
• pidx:referenceType