Prompted by #6873.

#1528 proposes removing status.experimental. I'm not ready to head down that path yet, but, in the mean time, I am prepared to improve the way we set the experimental status.

The schema docs describe status.experimental as:

a boolean value that indicates this functionality is intended to be an addition to the Web platform. Some features are added to conduct tests. Set to false, it means the functionality is mature, and no significant incompatible changes are expected in the future.

This text doesn't quite capture the meaning of the data as we've come to update it. For consumers, we should revise the wording to more clearly articulate the meaning of the true and false states; for contributors, we should write contribution guidelines for choosing between the two values.

Once these docs and the guideline are written, then we should start follow-up issues to clean up any data accordingly.

Tasks:

• Write new definition for experimental
• Write data guideline for experimental
• Open PR for new tooltip on MDN