By law, every single government form you're able to file is supposed to have an XML Schema available in a centralized registry. This regulation is widely ignored in practice, particularly by local / municipal governments.
This used to be more important in the past, as such a form could automatically / semi-automatically get an entry in the EPUAP form catalog and be made electronically fillable (EPUAP being the now-deprecated centralized government bureaucracy portal basically). As far as I understand, the way that worked was through XSLT and XML Forms. There was some weirdness about each document having a fillable / form view and a preview, I think XML Forms was somehow used to generate the XHTML form, while the XSLT sheet could only generate an XHTML preview of a complete, filled-in version. There were also some custom annotations for auto-fill and such, that was partly done by most documents relying on standardized schemas for entities like "person", "address" or "company".
Since we moved to E-Deliveries and lost a central place for these forms to live in, this is (AFAIK) a bit less important and less common, but internally, things are still XML. If you're filing something like an ID renewal application, even through a newer, more user-friendly frontend, it's still just XML underneath. If you sign something through podpis.gov.pl (the standardized e-signature solution for government paperwork), you can even download that underlying document, both signed and unsigned, and see what that XML is. The pre-signing document preview generated by that site still comes from the XSLT I believe. The signatures themselves are, unsurprisingly, also done via the XML signatures spec.
Incidentally, the European E-Delivery system itself also relies on XML, WSDL and Soap pretty heavily. For those unfamiliar and/or not in Europe, it's basically "email but for the government", with all the guarantees and legal obligations of physical mail, cryptographically-attested confirmation of receipt, proper identity verification and assurance, cross-provider address portability, deployed to a lesser or greater extend in many EU countries and set to replace physical mail.