The Confluence Metrics graphs are quite interesting! It would be great if the "Grace Period" could be better defined, in particular, how do you qualify the start of a grace period?

Is it when the defining standard reaches a certain level of document maturity? E.g. W3C Recommmendation or at least Candidate Recommendation?

Or given the qualification "can reasonably assume are still a part of the web platform", is it based on there existing some number of Web Platform Tests for the API, and 2+ browsers passing them (in the same way)?

Either way it would be great to have a (at least somewhat) measurable / objective criteria, especially since the graphs make it look like the data is quite precise.

Thank you for providing such a great resource!