In #123 it came up that default is RECOMMENDED as valid, but it seems as though a non-valid value here would actually not function as a default. As such, it seems as though we may want to harden the language here to MUST in order to protect defaults from resulting in invalid data.

The RECOMMENDED language in question is here: https://github.com/json-schema-org/json-schema-spec/blob/master/jsonschema-validation.xml#L622

P.S. Should #123 be accepted, to add the example keyword, it should probably also get this change to stricter language, for the same reasons.