Curious why YAML doesn't work for you?
I don't know of any language that supports YAML without a 3rd party library.
Is it merely about the ecosystem? I'm curious if something about the language isn't meeting people's needs.
The YAML spec is thousands of lines long (23k words, to be more exact). This is even longer than XML (20k words). JSON's spec is less than two thousand words. For a language that's supposed to be human-readable, YAML is maddeningly complex.
Plus, of course, you can execute arbitrary code with it. By design. AND it contains semantic whitespace, which is personally my least favourite innovation ever.