Checks cover XML well-formedness and a curated set of EN 16931 business rules (BR-*). Output follows the EN 16931 structure with consistent calculations. It is not a full XSD + Schematron validation — the Peppol endpoint scheme is inferred from country, and profile-specific rules still need checking. Full Schematron validation of real invoices is work we do.
A sample is a starting point. Getting real invoices to pass Peppol, XRechnung and country-specific Schematron — every time, at volume — is what we do.