I don't like NO as a boolean literal (mostly because it's also an ISO country code), but there's only one right way to parse it in a YAML 1.1 document. It was a

I don't like NO as a boolean literal (mostly because it's also an ISO country code), but there's only one right way to parse it in a YAML 1.1 document. It was a mistake to apply the 1.2 rules to 1.1 documents and issue a "warning" about incorrect output, rather than require rejecting the document if the 1.1 rules aren't implemented.