Factur-X EN 16931 from scratch: PDF/A-3 + CII XML in Node.js / TypeScript

France's e-invoicing reform kicks in September 1st 2026 . Germany's has been live since 2025. By 2027, every B2B invoice in the EU will be structured. Yet the amount of bad documentation around Factur-X — the hybrid PDF+XML format mandated in France and widely used in DACH — is impressive. Most "tutorials" either point you at a €5k commercial SDK or wave hands at 200 pages of XML schema. This post is the opposite: a working implementation, under 500 lines of TypeScript, zero paid dependencies, t