Support undocumented user/group/pull/123 and user/group/issues/123 format?

GitHub has documented autolinking at https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/autolinked-references-and-urls, but today I found another way that doesn't seem to be documented.

user/group/pull/123 and user/group/issues/123 appear to both expand if the issue or pull request exists, even if the text refers to a PR when it is an issue, or an issue when it is a PR. (I know that PRs are issues, but not "issues", but it was definitely unexpected to me that foo/bar/pull/123 would work when foo/bar#123 is a non-PR issue!)