Comment 1 for bug 1986660

Just to be clear: apt.conf(5) is not the definitive source, that is (fsvo reference) in /use/share/doc/examples/configure-index. The manual page only documents popular options whereas the index lists them all (apt test suite type checks against it).

Phased updates are documented in apt_preferences, but the documentation has not been updated for the new implementation either.

They are also, and primarily, documented in the discourse post as that was requested as the preferred documentation medium.