How to get warnings for non-transpilable CSS features?

[ifta-hop]

Using the browserslist setting in package.json, I can tell parcel to add vendor prefixes and use syntax lowering to support older browsers ( https://parceljs.org/languages/css/#browser-targets ). However, it looks like this is not possible for all CSS features; for example CSS Layers and CSS Grid seem to be left unchanged even if I specify IE 6 as target, which definitely doesn't support either. How can I make Parcel warn me in those cases.

The closest thing I found is the doiuse PostCSS plugin, but at least with a simple configuration as described in https://parceljs.org/languages/css/#postcss (see below), it seems to run on the source files before Parcel does its thing, and thus also warns on stuff Parcel can handle for me.

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To be clear, this is not a request or expectation to magically support every CSS feature in every browser, just a request to tell me when I (might) need to take action
Also, no, I'm not targeting IE 6, but this was an easy test case to see if Parcel would warn me that it's obviously not going to work

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postcss.config.mjs I used:

const warnedFeatures = new Set();

const config = {
    plugins: {
        doiuse: {
            browsers: ["IE6"],
            /**
             * @param {{ feature: string; message: string; }} usageInfo
             */
            onFeatureUsage(usageInfo) {
                if (!warnedFeatures.has(usageInfo.feature)) {
                    warnedFeatures.add(usageInfo.feature);
                    console.warn(usageInfo.message);
                }
            },
        },
    },
};

export default config;