But if it _might_ turn up, you have to assume it will and deal with it, and then you're into the exact same problem as before, but with something even less 'standard' than before.

I think it's like cryptography. Why bother to roll your own when there are people who are cleverer (certainly than me. I don't know about you) who've already put a lot of effort in to this, so just use one of the well tested standard libraries and don't mess with it