Let's be more explicit; we already have plenty of non-tentative things in testdriver which are not in either spec — #127 (final RFC) merely requires a WebDriver endpoint, not that it is in one of those specs.

Ah. I had assumed that the existence of a WebDriver endpoint implied it needed to be in the WebDriver spec. So how is WebDriver endpoint defined, given that Gecko uses Marionette for WPT and no other vendors implement this WebDriver endpoint yet?

For example, https://webbluetoothcg.github.io/web-bluetooth/#automated-testing defines a whole load of endpoints.

The policy is that it requires a spec for the endpoint, not that that spec be in any specific standard.

Thanks. Now I better understand your original question regarding whether an explainer is sufficient. I agree that at least having an explainer makes sense, so if the consensus is that an explainer is acceptable, we probably don't need this RFC. RFC 127 just says "an existing WebDriver endpoint", which isn't explicit about a formal spec, though I guess that could be inferred. So perhaps we still need an RFC making it clear that an explainer is sufficient.

That said, one difference between a spec and an explainer is that an explainer is far more likely to change than a spec. So that might still be one reason to mark these methods as tentative: to indicate that the details are still being ironed out.