KDL - a config language
There's a living specification, as well as various implementations. You can also check out the FAQ to answer all your burning questions!
In addition to a spec for KDL itself, there are also standard specs for a KDL Query Language based on CSS selectors, and a KDL Schema Language loosely based on JSON Schema.
The language is based on SDLang, with a number of modifications and clarifications on its syntax and behavior.
There are a ton of config languages beyond the big players of JSON and YAML, but I still think there's interesting work to be done in the field and none of them are entirely satisfying.
KDL looks interesting, and I like that it has a spec and a schema language right from the start.
via this toot