@microsoft-github-policy-service agree

We don't want to make any breaking changes to the custom data format, just additions.
The file is spec'ed and also used by other projects. So we want to keep the browsers as is.

So simply add a new 'baseline' (or `baseline-compatibility') property on the same level as browsers. The value set should be well defined, maybe an enum and a description. This can then go in the schema: https://github.com/microsoft/vscode-CSS-languageservice/blob/main/docs/customData.schema.json and also in the documentation.

https://developer.mozilla.org/en-US/docs/Glossary/Baseline/Compatibility

Thanks @aeschli. I've reverted the browsers change and added baseline to customData.schema.json. Is there a schema validator I can run to make sure it's correct?

If you open it in in VS Code you will get validation.
To validate an custom data file against your schema follow the steps here: https://code.visualstudio.com/docs/languages/json#_json-schemas-and-settings

Ok great, I've added this to my local settings and I can confirm that there are no validation warnings in browsers.css-data.json:

    "json.schemas": [
        {
            "fileMatch": [
                "**/web-data/data/browsers.css-data.json"
            ],
            "url": "/Users/rviscomi/git/vscode-css-languageservice/docs/customData.schema.json"
        }
    ]

Thanks @rviscomi !