Message

When Supplier is Greek, the MARK Number must be a positive integer

Context
cac:AdditionalDocumentReference[$isGreekSender and ( /*/cac:AccountingSupplierParty/cac:Party/cac:PostalAddress/cac:Country/cbc:IdentificationCode = 'GR') and cbc:DocumentDescription = '##M.AR.K##']/cbc:ID
Test
matches(.,'^[1-9]([0-9]*)')