My favourite character is the Greek question mark;
I like to imagine that sites like this have noticed the bug but have the sense of humor to choose not to fix it.
I've got my Emacs set up to display in "bold, fluo foregound and a dark background underlined by a pink line" (yes, literally that obnoxious) any character which is not part of a list of characters I consider to be acceptable. And it's configured to show any "zero width" character as if it had a width. So any "invisible character" as well as any "invisible zero width character" does appear as a black square, underlined with a pink line.
And that for any buffer/file.
https://gitlab.com/nervuri/nervuri.net/-/raw/master/gopher/z...
Looks like the only one Vim misses is U+17B5? Though it there could be more not listed there. Unicode is a deep dark forest.
----
For others readers, here's a non-gopher version of the article linked inside: https://nervuri.net/stega
avg=ㅤ=>ㅤ.reduce((ㅤㅤ,ㅤㅤㅤ)=>ㅤㅤ+ㅤㅤㅤ)/ㅤ.length
avg([3,1,4,1,5])
2.8
It doesn't do much on its own. I feel like it could, but the most effective use case I've come up with it you can invisibly plant a piece of code in some piece of text, then later on run another script that looks for that piece of code and runs it. I'm guessing that splitting the code up like this would make it harder to detect (not to mention that this code could even reside in other programs' comments undetected).
I think the best solution to this type of problem would be a clipboard utility that warns you when you copy text which contains hidden characters, homoglyps, rarely used whitespace characters, etc.