UBL-SR-53
CompanyID (VAT Identifier) must be stated when providing the PartyTaxScheme/TaxScheme/ID.
What the rule checks
As the rule set's publisher wrote it. The rule runs on every element the context matches, and fails where the test is false; the validator reports the line of that element.
cac:PartyTaxScheme
exists(cac:TaxScheme/cbc:ID) and exists(cbc:CompanyID)
Checked with EN 16931 Invoice (UBL), EN 16931 Credit Note (UBL), Croatia eRačun Invoice (UBL), Croatia eRačun Credit Note (UBL)