> I think the main point here is that the context/prediction model of JPEG XL's modular mode is expressive enough to consider it a kind of mini-programming lang

> I think the main point here is that the context/prediction model of JPEG XL's modular mode is expressive enough to consider it a kind of mini-programming language which is 'Turing-complete' (with some asterisks like requiring infinite images). Yes, this is exactly the point I intended. I have added a link Gwern Branwen's https://www.gwern.net/Turing-complete https://www.gwern.net/Turing-complete for context. (I considered adding a note on how no physical computer or interpreter running on one is really Turing-complete before submitting the story but decided against it, because the context should convey the asterisks on "Turing-complete".) I have also quoted your paragraph on security on the page. Something I did not consider was that people may link to my page to support security FUD against JPEG XL, a format I like and look forward to adopting. I hope this is sufficient mitigation.