My thoughts exactly. YAML is a superset of JSON that already has all this stuff and more.

I actually had no idea that YAML is a superset of JSON. Thanks! I'll look into it.

For the same reason sexps weren't good enough, apparently.

Partly because JSON has the lovely feature of being able to just eval() it into an object in browsers.

That's not really a lovely feature in this day and age. If anything it's an unfortunate artifact, as the right way to deserialize JSON is JSON.parse().

That's not the right way to parse JSON, it's really insecure

And slow, JSON.parse is magnitudes faster than using user-javascript to parse it yourself.