An unknown or uninterpretable field was present.
An unknown or uninterpretable field was present. Stock rojoma-json
decoders only return this for maps whose keys are rejected by
the FieldDecode, but user codecs can use it to reject unknown
fields if desired.
An array with the wrong number of elements was found.
A value was found in the correct position but of the wrong type.
A value of the correct JSON type was found but it held undecodable value.
A required field was missing.
There were several choices and they all failed.