I think the point is that they accept more than the spec dictates - do your JSON parsers accept e.g. the vs code config file (JSON with comments) or JSON with unquoted keys?
The most commonly used parsers only accept valid JSON - including the one included within most JS runtimes (JSON.stringify/parse). VSCode explicitly uses a `jsonc` parser, the only difference being that it strips comments before it parses the JSON. There's also such thing as `json5`, which has a few extra features inspired by ES5. None of them are unquoted strings. I've never come across anything JSON-like with unquoted strings other than YAML, and everything not entirely compliant with the spec has a different name.
