It's hardly answers the question, as strictly speaking there's no such thing as "metadata". Everything you can pass to another person can be described as "data"

It's hardly answers the question, as strictly speaking there's no such thing as "metadata". Everything you can pass to another person can be described as "data", whether it is a color of your coat or the statement that you are describing the color of your coat. Basically, you can think of any attribute of an object as "metadata" as long as it can be only one per object and doesn't have any attributes itself, and both things can change easily and depend on the point of view. On the contrary, I don't remember one single case when the object was described easily using "node/attribute" separation, but couldn't be described as easily using JSON. In fact, I don't even think it's possible, as you can always make two children for each object: "attributes" and "nodes". So I guess it actually is unnecessary complication and not the benefit of using XML over JSON.