This is not interesting in the way that "DNS parsing is turing complete" is interesting. Nobody can send you a unicode file and make you run an infinite loop or whatever.

Within Unicode is defined a DSL used internally by the library implementers to define some business logic, like most DSLs it is turing complete. Anyone with the ability to make you run their rules file already has the ability to make you run arbitrary code (it's a software vendor for software you use).

It's still always fun to find Weird Machines, but as they go, this one is not very weird (it's one of the known families of programming languages, the Mathematica language being the most well known example. The person who specified this most likely was aware that this is turing complete and it's the rules author's responsibility not to write infinite loops).

So... Who's porting Doom to run on this?

I've been wondering for a while if anything in Unicode could accidentally compute. It turns out that UTS #35 transliteration rules are Turing-complete. I show how to compute Collatz with just 3 rewrite rules running on stock ICU.

At this point it feels more difficult to ensure that your format cannot compute than to ensure it can

Does the Latin-Katakana example given imply that some input value can cause it to not terminate?

reminds me of Word's autocorrect being turing-complete https://www.youtube.com/watch?v=jlX_pThh7z8 (3:57, but whole video is fun)

Does this mean I could post some untransliterated text here in a comment and make your browsers all do these computations?

Waiting for someone to vibe a compiler targeting Unicode transliteration rules...

reminded me of the PowerPoint Turing Machine

https://www.youtube.com/watch?v=uNjxe8ShM-8

Who implements transliteration rules? I assume operating systems? Or text renderers?

Does it work on modern OS or just PyICU ?