Message

Value MUST be part of code list 'Recommendation 20, including Recommendation 21 codes - prefixed with X (UN/ECE)'.

Context
/ubl:DespatchAdvice/cac:Shipment/cbc:GrossVolumeMeasure
Test
not(@unitCode) or (some $code in $clUNECERec20 satisfies $code = @unitCode)
Code lists
Recommendation 20, including Recommendation 21 codes - prefixed with X (UN/ECE)
Usage
/ ubl:DespatchAdvice / cac:Shipment / cbc:GrossVolumeMeasure / @unitCode