In the json encoding structures (and also some built-in types like NodeId) are encoded as json objects, which are key-value pairs without ordering. For the binary and XML encoding however the order of fields in structures is important and must be preserved and also in the examples for json encoded values the order is always the same as in the definition. This could easily lead to the impression that json objects are ordered, however a decoder relying on the order would not be correct and could be incompatible with certain encoders.

Thus the json description should explicitly state that json objects are of arbitrary order and decoders cannot rely on the order given by the datatype definition.