XML syntax is bad, but yaml doesn't have a proper blessed batteries-included built-in schema language afaik. A well formed XML with an xmlns will have validation and autocomplete in a good editor thanks to this. JSON can do it too. Never seen it done with yaml.

It's a pretty big frustration in a language that is so slow to test -- commit push run wait find the error oh I made a typo. Better code-time validation fixes this but the tooling for that in yaml is weak.