[array_key_first]

XML is perfectly fine. What are these alternatives?

YAML is just bad. JSON is harder to read for deeply nested structures. TOML and the like don't have enough features.

[RHSeeger]

XML is pretty fantastic for a lot of things that JSON is not up to the task for. And YAML ... has it's own, special issues.

[sham1]

Maybe ASN.1? Although that has an official XML encoding so maybe not.