But my case was with a yaml validated to a schema. A kube ingress file with a list of rules. My additional dash made it a new entry, in practice allowing everything. With xml it would have been very explicit that I now accidentally had made two rules.
XML has them sorta built in (basically all (notable) libraries support them), but it's not like it's required or somehow innately protected because of that. It's just a bit easier to adopt.