IMHO, the complexity that this would introduce just highlights why it's a good idea not to have them. > "but I think it would be legal to reject JSON with dupl

IMHO, the complexity that this would introduce just highlights why it's a good idea not to have them. > "but I think it would be legal to reject JSON with duplicate keys." No it would not. `SHOULD` has a very specific meaning: SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course. See http://www.ietf.org/rfc/rfc2119.txt http://www.ietf.org/rfc/rfc2119.txt An object with duplicate keys must be parsed, but the exactly result will be implementation specific (undefined).