Our shop are heavy users of YAML, and we've sort of backed our way into a restricted subset of YAML. Some of them are config files, but others function closer to DSLs.

I have not yet taken a look at strictyaml, but after years of use the spec definitely needs YAML, The Good Parts Treatment.

One thing the author did not mention was how slow the out of box the Python YAML parser can be. This can be sped up with a call to libyaml, but then you lose the safe_load method.