Author here. Short version is that YAML 1.1 behavior has a lot of bad, but the 1.2 spec addressed the major problems (way back in 2009!). I don't really know why PyYAML never updated to 1.2. So for the intervening years Python users kept hitting 1.1 bugs and blaming the format.

I wonder if YAML is better than JSON for LLMs, because the indentation keeps the nesting level information local to the content.

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