The outermost level of a JSON document is either an "object" (curly braces) or an "array" (square brackets).
Any software that converts JSON to XML has to reconcile the fact that they are different data models with different rules. Different conversion tools handle these differences in different ways.
UPDATE (2021-09-03): As noted in the comments, subsequent iterations on the JSON specification allow the outermost level to be a string, number, boolean, or null.
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