> An object structure is represented as a pair of curly bracket tokens surrounding zero or more name/value pairs. A name is a string. A single colon token follows each name, separating the name from the value. A single comma token separates a value from a following name. The JSON syntax does not impose any restrictions on the strings used as names, does not require that name strings be unique, and does not assign any significance to the ordering of name/value pairs. These are all semantic considerations that may be defined by JSON processors or in specifications defining specific uses of JSON for data interchange.

https://www.ecma-international.org/wp-content/uploads/ECMA-4...

This wording allows a particular implementation to define its own meaning to the order of key-value pairs, or even to produce a multimap.