See T10939#175656 for some context.
If you own /webroot/ but don't care about /webroot/intern/, you may have a package on /webroot/ which has weak dominion and cedes ownership of /webroot/intern/ to another package. Normally, this keeps you off the notification list for stuff happening in /webroot/intern/.
In some cases, a sweeping change may hit both packages, and you may want to use your authority over all of /webroot/ to clear a block from /webroot/intern/. You can normally already do this by just removing the package as a reviewer, but the intent isn't clear, the fact that it's procedurally OK for you to do this isn't made clear, and it isn't very convenient and it can be re-added later depending on how Herald and Owners are set up.
After T12271, we can offer a way to extend your authority and clear this at "Accept" time:
Accept Revision: [√] As epriestley [√] As "Webroot" [ ] (Force Accept) As "Webroot/Intern"
Language could probably be a little more clear. These "extended authority" accepts would be unchecked by default.
If either of these rules are contentious or violate a bunch of federal regulations or something, we can alternatively just do an explicit "These Users, Packages and Projects have extended authority to audit and review on behalf of this package: [ A, B, C ]", which you must list explicitly for each package which is procedurally contained by another package rather than using the actual path definitions.
This rule (explicit list) is better from my point of view since I think the empirical path-based rules will hit some unintuitive edge cases, but I'm not sure how realistic it is to get sub-packages to properly whitelist containing packages.