Annotate features which can be used safely without support

In webhint we've recently started integrating BCD to automatically warn users about potential cross-browser support issues.

Lately we've been focusing on reducing noise from features developers can/should use even if not all their target browsers support them. In the short term we've started building our own "ignore" list, but adding an annotation to BCD itself would better help other tools utilize this same logic.

I'm not tied to a specific name (maybe safe or progressive), but something to indicate that a feature degrades gracefully and doesn't require cross-browser support or a polyfill to use today (on a related note it may also be interesting to annotate when a feature has a viable polyfill available).

I realize in some cases this could prove to be fairly subjective, but I think asking "would a reasonable developer use this in production without providing any explicit fallback or alternate handling?" could help, especially if it's supported by real-world examples.

Some examples we've run into so far include cursor in CSS (not supported by some old Android versions still in use) and integrity in HTML (as using subresource integrity is a good idea even if not all your target browsers support it). CSS in particular likely has many more candidates we'll identify as we keep testing more web content.

Thoughts?

No files, tests, or entry points are named in the issue. Start by resolving the proposed annotation's name and criteria using the cursor and integrity examples; done means BCD has an agreed annotation that tools such as webhint can use to identify features safe without fallbacks.