What is XSD validation?
Short answer
XSD validation is a technical check in which the XML document is compared with the prescribed XSD schema. The abbreviation XSD stands for XML Schema Definition. The XSD schema determines what structure an XML document can contain, which elements and attributes
Basic condition
Even before XSD, XML must be well-formed at all — correctly closed tags, namespace, quotes, one root element.
Structure, not just order
Mandatory occurrence, frequency, data types, order and permitted place of the element according to UBL 2.1 XSD.
Business logic
XSD itself does not know whether the sum of VAT, BuyerReference or the rules of EN 16931/Peppol BIS/Slovak transpositions fits — that's what Schematron is for.
No custom XSD
Peppol BIS Billing 3.0 does not publish its own XSD — it is a CIUS over EN 16931 that uses the existing OASIS UBL 2.1 syntax base.
Conclusion
XSD validation is a technical check of an XML document against a prescribed schema.
Act No. 222/2004 Z. z. Coll. about VAT · FAQ of the Financial Administration of the Slovak Republic from 7 July 2026 · Peppol BIS Billing 3.0
Not legal advice. Machine-translated answer, not yet manually reviewed. For the exact wording, see the Slovak original.