incumbent settings object is utilized in several places in the spec, although there's this warning in the HTML spec here (scroll down below the example):
Warning: The incumbent and entry concepts should not be used by new specifications, as they are excessively complicated and unintuitive to work with. We are working to remove almost all existing uses from the platform: see issue #1430 for incumbent, and issue #1431 for entry.
Should this spec be using the relevant settings object instead?