Greek suppliers must provide their Seller Tax Registration Number, prefixed by the country code
GR-S-011
cac:AccountingSupplierParty[$isGreekSender]/cac:Party
count(cac:PartyTaxScheme[normalize-space(cac:TaxScheme/cbc:ID) = 'VAT']/cbc:CompanyID)=1 and substring(cac:PartyTaxScheme[normalize-space(cac:TaxScheme/cbc:ID) = 'VAT']/cbc:CompanyID,1,2) = 'EL' and u:TinVerification(substring(cac:PartyTaxScheme[normalize-space(cac:TaxScheme/cbc:ID) = 'VAT']/cbc:CompanyID,3))