Earlier quoted context omitted.
> The purpose of AGENTS.md—to make metadata about a project available in a structured format AGENTS.md is not "structured format", then it'd be JSON or YAML or some other fucked up format instead. Currently at least, it's fully freeform and you can put whatever there, agents will do there best to follow it.
Markdown is still a structure. It may be a very loose one, but it still enables a reader (of any flavour) to, for example, determine which parts of the text are code and which aren't.
> determine which parts of the text are code and which aren't
With this argument you'd could claim ASCII/plaintext is "structured data" too, just group code with "===" and that's evident. Obviously that doesn't make a format "structured data".