Implementations do not show the inherited documentation

(api.drupal.org is still running on Drupal 7; the 1.x branch is for Drupal 9.)

Methods in instance: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Routing%2...
Methods in interface: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Routing%2...

This connection is done in the "api" module. Moving this issue back there.

I don't quite understand what this issue is reporting, but it looks like {@inheritdoc} is not working. Child class method pages don't show the annotations from the parent class method. Is that this issue?

I think 📌 Information is missing from the API pages Active might be related (or even the same but not sure until I check in detail).

They seem the same issue, as in both the cases the class implements an interface, which contains the method descriptions that should be shown for the class itself.

Yes, either 📌 Information is missing from the API pages Active is a duplicate of this, or I need to find/create another issue for API, or it's not an API issue (seems unlikely).

I don't know if it is strictly about interfaces. We would have to find a class that extends another class and overwrites a parent class function not defined in the interface. I have done some searching but that's tricky to find.

This information is missing from the 9.x API documentation as well now, for what that's worth.

This seems like a serious problem, in that most of the pages we look for in the API are implementations of something else, and because of whatever problem there is, none of them document their parameters, return values, etc.