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That's forwards compatibility.

Backwards compatibility: New versions of the software can use the files from old versions.

Forwards compatibility: Old versions of the software can use the files from new versions.

If you switch from JSON to JSON5, the new version can use the config file from an old version. If you switch from JSON to TOML, your users have to create a new config file, or you will have to support both JSON and TOML.

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The software maybe backwards compatible, but the format is not backwards compatible as old software (expecting JSON) cannot parse the JSON5 format.

I'm not going to argue about that, since I never claimed that JSON5 is backwards compatible with JSON. I said software can move from JSON to JSON5 without breaking backwards compatibility. If you want to claim that JSON5 is forwards compatible but not backwards compatible with JSON, that's fine by me.

Makes sense, thank you!

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