For Danish Suppliers PaymentID is mandatory and MUST start with 01#, 04# or 15# (kortartkode), and PayeeFinancialAccount/ID (Giro kontonummer) is mandatory and must be 7 or 8 numerical characters long, when payment means equals 50 (Giro)
ubl-invoice:Invoice[$DKSupplierCountry = 'DK' and $DKCustomerCountry = 'DK']/cac:PaymentMeansnot((cbc:PaymentMeansCode = '50') and not(((substring(cbc:PaymentID, 1, 3) = '01#') or (substring(cbc:PaymentID, 1, 3) = '04#') or (substring(cbc:PaymentID, 1, 3) = '15#')) and matches(cac:PayeeFinancialAccount/cbc:ID, '^[0-9]{7,8}$') ) )