Ionite wrote the SI-UBL 2.0 validation artefacts, a schematron and XLST2 scheme that can validate SI-UBL 2.0 documents, as well as the country-specific rules for the Netherlands in Peppol BIS 3.

Ionite has extensive experience with Schematron and document validation, and we can develop schematron validation for other document formats as well.

You can get the validation artefacts at the Github page of the Netherlands Peppol Authority.