To produce an attribute, not a child element: the JSON key must start with @ — "@lang": "en" on a node becomes lang="en" on that node's XML tag. A #text key becomes the element's text content alongside its attributes. Any other key, including ones that merely look attribute-like, is emitted as a nested child element instead. The converter also refuses non-object input outright — an empty object or a bare array at the root throws "JSON object is empty" rather than silently producing empty XML.