RFC 011 - "Pay-for-Standard" dependency

[cyberphone]

The "default" receipt format is based on a CEN standard which you apparently must purchase.
Although there is a JSON schema, it seems a bit insufficient as sole documentation.

I find this slightly concerning for a mass-market solution.

How much can you describe without breaking the copyright?

Have you considered PDF? It is close to a de-facto standard for e-receipts. Anyway, whatever format you use, a wallet should support a PDF export method.