XML is beloved by tax authorities. The Polish tax authorities really love their e-documents and online filing. Except their XML documents are completely human-unreadable, since the schemas are based on field numbers in paper forms. Even in the brand new National e-Invoicing System, designed from scratch, with no paper forms, most fields have names like ‹P_19N›1‹/P_19N›. You read the XML schema to find out it is a "Marker of lack of delivery of goods or provision of services exempt from tax under Article 43 paragraph 1 of the [VAT] Act, Article 113 paragraphs 1 and 9 of the Act or regulations issued under Article 82 paragraph 3 of the Act or under other provisions" (Google Translated, because of course everything is in Polish). So my invoice is saying "yes [1], I am not [N] exempt from tax under $allThatNonsense [P_19]".

In unrelated news, the main author of the VAT Act is offering tax consulting services, as Registered Tax Advisor #00001.