When it comes to human-editable config and data files, XML and JSON are human-unfriendly, INI syntax is limiting and unspecified, and YAML has some nice ideas that don't scale up to medium-sized documents, le alone large ones (trust me, I've spent a lot of time wrestling with Ansible playbooks).

So far, my favourite contender has been TOML (nearly as rich as JSON, much more human-friendly to write) but today I came across a thing called OGDL, the Ordered Graph Definition Language. The data-model is super-minimalist: the basic syntax produces an ordered tree of byte-strings, and there's an optional second pass that interprets some nodes as references back into another part of the tree to make a fully general directed graph. Since the data-model is simple, the syntax is deliciously simple too: write a word on a line, if the word on the next line has a greater indent, it's a child; if it has the same indent, it's a sibling, etc.

I don't think I'd want to make it my standard config file format yet (for one, there's no Python library for it), but it's something I need to keep in mind for the future.