Right, didn't think about it in these terms.

I've tried printing `input.encoding` and `input.valid_encoding?` (with this patch not applied):
MRI 1.9.3 prints `<Encoding:ASCII-8BIT>` and `true` respectively.
RBX prints `<Encoding:ASCII-8BIT>` and `false` respectively.

Both pass the test. Don't know what to make of this, do you have any ideas?