CPAN link provided by the parent says 1.2 still isn't a superset:
> Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even though the incompatibilities have been documented (and are known to Brian) for many years and the spec makes explicit claims that YAML is a superset of JSON. It would be so easy to fix, but apparently, bullying people and corrupting userdata is so much easier.
"Please note that YAML has hardcoded limits on (simple) object key lengths that JSON doesn't have and also has different and incompatible unicode character escape syntax... YAML also does not allow \/ sequences in strings"
> Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even though the incompatibilities have been documented (and are known to Brian) for many years and the spec makes explicit claims that YAML is a superset of JSON. It would be so easy to fix, but apparently, bullying people and corrupting userdata is so much easier.