[nonchalance]

The JSON RFC (http://www.ietf.org/rfc/rfc4627.txt?number=4627) says

    The names within an object SHOULD be unique.

SHOULD is defined (http://www.ietf.org/rfc/rfc2119) as

    3. 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.

Salient point is that you would need to ensure that you are only using JSON parsers that tolerate duplicate names (and use the last value)

[IanCal]

> Salient point is that you would need to ensure that you are only using JSON parsers that tolerate duplicate names (and use the last value)

To drive this home a bit more forcefully, it requires knowing the behaviour of your parser where it is marked as "undefined" in the spec.

If that isn't enough to stop you, DON'T USE JSON. A patch level change in a library could break your code in a non-obvious way and it would be your fault. If you want comments, DON'T USE JSON, JSON DOESN'T HAVE THEM.

[bzbarsky]

Note that if your parser is the ES-standard JSON.parse, then the behavior here is in fact defined by ES5 section 15.12.2, even with duplicate names.

[juandopazo]

And the big point here is that the members of the RFC group were considering breaking the EcmaScript standard and change it to MUST which would break existing programs and the "workaround" in the article.

[tonyg]

I wish they had! I wonder why they didn't? JSON is already a subset; limiting it to non-duplicated keys would just tighten it a little.