In my mind it's one thing to let a string control whitespace a bit versus having the ability to write any string in a non-renderable format. Can anyone point me to some more information about why this capability even exists?
If you have a text encoding with two invisible characters, you can trivially encode anything that you could represent in a digital computer in it, in binary, by treating one as a zero and the other as a one. More invisible characters and some opinionated assumptions about what you are allows denser representation than one bit per character.
Of course, the trick in any case is you have to also slip in the call to decode and execute the invisible code, and unless you have a very unusual language, that’s going to be very visible.
It's just a custom string encoder/decoder whose encoded character set is restricted to non-printables.
Many editors and IDEs have features (or plugins) to detect these characters.
VSCode: https://marketplace.visualstudio.com/items?itemName=YusufDan...
VIM: https://superuser.com/questions/249289/display-invisible-cha...
Many LLMs can interpret invisible Unicode Tag characters as instructions and follow them (eg invisible comment or text in a GitHub issue).
I wrote about this a few times, here a recent example with Google Jules: https://embracethered.com/blog/posts/2025/google-jules-invis...