Baseline acts as a flag that tells this feature is supported across browsers.

But there is a few critics:

• Baseline doesn’t take all the browsers they need to support into account
• The safest Baseline stage — Baseline Widely Available — doesn’t cover old enough browser versions, which they still support
• Baseline says nothing about whether a web feature comes with accessibility challenges or no
• Baseline doesn’t tell web developers if it is OK to use a feature that’s not Baseline yet, perhaps as a progressive enhancement, or by using a polyfill.

Here are the definition of a traffic light-style:

• Not Baseline, if a feature is not yet supported on Chrome (desktop and Android), Safari (macOS and iOS), Edge, Firefox (desktop and Android)
• Baseline Newly Available, if it’s supported on the above browsers
• Baseline Widely Available, if it’s been supported on the above browsers for more than 2.5 years

Perfecting baseline: accessibility, flag progressive enhancement, polyfills and best practices; extend browsers and browsers versions to allow configure which (other) browsers should be taken into account.