# Schematron

XSLT-based rule language used by KoSIT and Peppol to validate business rules in XML invoices.

## Definition

XSLT-based rule language used by KoSIT and Peppol to validate business rules in XML invoices.

## Explanation

Each rule (assert/report) carries an ID like BR-DE-15 or PEPPOL-EN16931-R046, which appears in validator output.

Schematron complements XSD: schemas check structure and types, Schematron checks cross-field arithmetic, conditional requirements, and code-list constraints.

## Related resources

- [KoSIT validator errors](/resources/kosit-validator-errors)

## Related terms

- [KoSIT](/resources/glossary/kosit): German coordination body; commonly refers to the BR-DE validation rules/validator for XRechnung.
- [Validation](/resources/glossary/validation): Process of checking an e-invoice against syntax rules and business rules.
- [XML Schema (XSD)](/resources/glossary/schema): A formal definition of allowed XML structure and data types.