Comment by deaddodo

"Structured" in this case refers to being able to be directly mapped to a data structure. Think protobuf and other similar transport mechanisms. The recipient knows what structure to expect because it's not a valid XML document if it's breaking those constraints.

JSON is not, it is closer to the PHP, JS, etc "object" type, which is an ephemeral object with arbitrary member associations.

And, to be clear, this is not a value judgement. They just excel in different fields. XML tends to be easier for strongly and strictly typed languages such as C/C++, C#, Java, etc where you can use the schema to generate your structs automatically. Vanilla JSON is easier for higher level languages that don't require you to manually create a mapping/validation level. JSON Schema tries to bridge that gap to a degree, but isn't built into the standard and isn't even universal.

But, ultimately, both are perfectly sufficient for either use case. It just depends on how much massaging you want to do to make them work.