[jcelerier]

> How should programs display it

what's wrong with foo����.txt

> or even address such a file? ... by using the array of bytes ?

[colejohnson66]

The fact that if one has two files, say “test{invalid bytes}.txt” and test{other invalid bytes}.txt”, both have replacement characters inserted at the same spot and would decode to the same codepoints.

[ygra]

It's ambiguous, for example.

[jcelerier]

so are a file named Hello.txt and another one named Нello.txt