UTF-8 characters in POSIX shell script *comments* - anything against it?

I would like to include a couple of non-ASCII characters in my POSIX shell script **comments**. Note this is in no way a duplicate of e.g. "Which character encodings are supported by posix?" as I care for the comments section only. Therefore I don't care if I can use Unicode for actual coding. I care if all shells which are POSIX-compatible will be able to read my file, or if some fail due to non-ASCII encoding. So, my editor (VS Code), will save such a file with UTF-8 encoding. Here are two files identified with the file utility (unsure if it cares for BOM):

$ file script1*
script1:     POSIX shell script, ASCII text executable
script1.utf: POSIX shell script, Unicode text, UTF-8 text executable

Question is, if POSIX shell scripts must be in ASCII only. Can't find anything relevant on this topic. Thank you.