The popularity of the target isn't as really relevant here as the capability of the target. XML supports annotated trees (attributes + child nodes) whereas most

The popularity of the target isn't as really relevant here as the capability of the target. XML supports annotated trees (attributes + child nodes) whereas most popular modern interchange formats only support one of those dimensions (child nodes). Some of them do support types that xml lacks (integers, null, etc.) but these can be annotated in xml so the lack isn't critical. Ultimately what all that means is that all e.g. json documents can be represented losslessly in xml, whereas the reverse is not true without explicit external schema. Which means targeting XML covers other less capable interchange formats implicitly.