Of late I have grown fond of ... brace yourself ... RDF in turtle format for config files. Supports comments, multiline literals, built-in support for references, and rich typing via xsd casting when necessary e.g.
ex:subject ex:createdOn "2002-01-24T12:00:00.000Z"^^xsd:dateTime ;
You can have no namespace (:subject :name "foo") or one or more to help separate metadata and structure (the config structure) from actual config data (ex:myInstance config:logfile "pathname to file"). And of course, all the metadata itself is labelable and can carry comments and descriptions so the config is essentially self-documenting. Or at least there is a standard, straightforward way to extract and organize the labels and comments if time has been taken to add them.