Now it's also true that JSON doesn't specify an entity that can be either an object or an array but not be a string or a bool or a number or null. So it's kind of true that JSON doesn't say that an object or array are valid root elements.

But JSON also says "JSON is built on two structures" - arrays and objects. It defines those two structures in terms of 'JSON values'. But it's a reasonable way to read the JSON spec to say that it defines a concept of a 'JSON structure' as an array or object - but not a plain value. And then to assume that a .json file contains a JSON 'structure'.

Basically... JSON's just not as well defined a standard as you might hope.

edit: And now I'm going to well actually myself: Turns out https://tools.ietf.org/html/rfc4627 defines a thing called a 'JSON text' which is an array or an object, and says that a 'JSON text' is what a JSON parser should be expected to parse.

So - pick a standard.