How Do You Interpret BCD "Fully Supported"?

[lolaodelola]

Every MDN reference page has a browser compatibility table at the bottom of the page which says the support status for the feature across browsers.

The browser compat table for <example-feature> looks like this:

Feature	Chrome	Edge	Firefox	Opera	Safari
example-feature	✓ 1	✓ 12	✓ 1	✓ 15	✓ 1

✓ indicates "Full support" since the specified version number.

[tunetheweb]

As always "it depends" 😀

While ideally it's all nice and easy for the simple case and when the spec and implementations agree, it gets complicated quickly — especially when the the spec and implementations disagree AND even more especially when a spec expands to add new sub-features.

For example, I don't think a feature should automatically revert to "partially supported" as soon as a new sub-feature is added. That way lies stagnation and irrelevancy. Not to mention it's not a useful signal for the web developers. This is where looking at the other features in the same table matters. So the first entry is the top-level support which often means "basic use case supported" or "original spec supported".

Similarly if there's part of a spec that has never been supported by any browser (or an optional part of the spec), but they all broadly support the basic use case then In would expect to see "fully supported". Of course in both cases there ideally would either be a spec update and/or additional BCD keys to explain this discrepancy but that's not always the case (and I say that as someone who writes and even owns some specs and tries his best to maintain them!).

I would also only use "partially supported" for when there's a missing key feature or has a bad bug that web developers need to be aware of. Not for some newer sub-feature. Nor for some obscure, rarely used, edge case where it technically diverges from the spec but not in a way likely to impact developers. But that takes some nuance that's difficult to mandate cleanly.

Plus I think specs are often written for implementors (browser vendors) rather than for end developers. Some of them are VERY difficult for lay men/women to follow (me included and I help write some of them!).

So TLDR: I take it to mean: "It means the feature is available in the browser, and works as the specification MDN describes" aka "as the average web developer would expect it to work".

Full disclosure: I work for a browser vendor (Chrome) and contribute regularly to MDN and specs.

[Sheraff]

As long as Safari is not evergreen like the other ones, a broad bucket like "Fully Supported" changes nothing to how i read the table. I look at the safari version, and then look up its release date, or look for it in browsersl.ist

[lolaodelola]

Thanks for sharing!

Just to let you know browsersl.ist uses CanIUse for the data it provides for web platform features. CanIUse, Baseline & these MDN support tables share the same source which is Browser Compat Data (BCD).

Edit: I'm also a bit confused by what you mean by "broad bucket". "Fully Supported" only refers to one browser at a time, it's what the tick the MDN support table means.

[Sheraff]

I think i confused this for the "Widely Available" baseline thing

[lolaodelola]

Ah! Easy mistake to make.