You don't need a new definition, you just need to follow the official Unicode security guidelines.
I recommend the Moderate Restrictive Security profile for identifiers for mixed scripts. TR39. Plus allow Greek with Latin. This way you can identify Cyrillic, Greek, CFK or any recommended script, but are not allowed to mix Cyrillic with Greek. And you still can write math with Greek Symbols.
What we don't have are a standard string library to compare or find strings. wcscmp does not do normalization. There is no wcsfc (foldcase) for case insensitivity. There's no wcsnorm or wcsnfc.
I'm maintaining such a library.
coreutils, diff, grep, patch, sed and friends all cannot find Unicode strings, they have no string support. They can only mimic filesystems, finding binary garbage. Strings are so rthi g different than pure ASCII or BINARY garbage. Strings have an encoding and are Unicode.
Filesystems are even worse because they need to treat filenames as identifiers, but do not. Nobody cares about TR31, TR39, TR36 and so on.
I recommend the Moderate Restrictive Security profile for identifiers for mixed scripts. TR39. Plus allow Greek with Latin. This way you can identify Cyrillic, Greek, CFK or any recommended script, but are not allowed to mix Cyrillic with Greek. And you still can write math with Greek Symbols.
What we don't have are a standard string library to compare or find strings. wcscmp does not do normalization. There is no wcsfc (foldcase) for case insensitivity. There's no wcsnorm or wcsnfc. I'm maintaining such a library.
coreutils, diff, grep, patch, sed and friends all cannot find Unicode strings, they have no string support. They can only mimic filesystems, finding binary garbage. Strings are so rthi g different than pure ASCII or BINARY garbage. Strings have an encoding and are Unicode.
Filesystems are even worse because they need to treat filenames as identifiers, but do not. Nobody cares about TR31, TR39, TR36 and so on.
Here is an overview of the sad state of Unicode unsafeties in programming languages: https://github.com/rurban/libu8ident/blob/master/c11.md