WPT details: Web Platform Tests under the /feature-policy/ directory are being rewritten to use the new header, to verify that it works as well as the old one. New tests are added for the header behaviour change as well. Other feature tests which integrate with the policy mechanism will similarly be changed to use the new header, if they used the old one previously.
The Permissions-Policy HTTP header replaces the existing Feature-Policy header for controlling delegation of permissions and powerful features. The header uses a structured syntax, and allows sites to more tightly restrict which origins can be granted access to features.
The Feature Policy API was recently renamed to "Permissions Policy", and the HTTP header has been renamed along with it. At the same time, the community has settled on a new syntax, based on Structured Field Values for HTTP.
Docs: https://github.com/w3c/webappsec-feature-policy/blob/master/permissions-policy-explainer.md
Explainers: https://github.com/w3c/webappsec-feature-policy/blob/master/permissions-policy-explainer.md