The Debian Policy Manual was never properly updated to reflect either the outcome of the Debian systemd packaging hoo-hah or the switch to systemd as the installed-by-default init system in Debian 8.
It describes things as if van Smoorenburg init and rc were still the defaults, fails to account for differences and obsolescences introduced by systemd, and treats alternative init systems (including systemd!) as mere addenda.
In 2014, at the tail end of the hoo-hah, I attempted to rectify this. I wrote a modified policy and sent it off to Russell Nelson for passing along to the policy people. Unfortunately, it apparently got lost in the shuffle when M. Nelson resigned from the Debian Technical Committee. So here it is.
policy.sgml.patch is the patch to the SGML source of the policy document.
Chapter 9 is what the patched policy looks like as a WWW page. Here is section 9.3 in particular.
(In August 2016, I drew attention to this on the Debian Policy mailing list with reference to Debian bug #835520 which I had noticed had been raised a couple of days earlier. The sole public response was a rather daft one asking whether I had discussed this on that very same mailing list that I was right there discussing it on, claiming that a bug needed to be raised when the bug that had already been raised was in the subject line of the message, and claiming that the work of writing was not done when there was an actual patch with an entire revised chapter of concrete text right here. To this day, Debian policy still primarily talks about runlevels and treats the default installed system as an "alternative" in an addendum.)
The patch only alters §9.3 of the Manual and its footnotes.
I have adhered to a few self-set rules here:
Policy must be actionable. The primary consumers of this are people raising release critical (and other) bugs and release engineers evaluating problems and their severities. So this revision doesn't include anything that would not result in actionable bug reports, including style guidelines and tutorials. There is most definitely room for tutorials on this stuff, as other people attempted to write in 2014 (and never finished), but the Manual is not the place for it.
Policy is neutral.
The Debian community strongly expressed an opinion, time and again, that although the Technical Committee had chosen systemd as what installs by default, that does not by itself deprecate or exclude other systems.
Like the Debian Policy approach to /bin/sh, this patch attempts to address init systems in terms of generally-applicable things that developers and users should obtain from them.
Things that are specific to individual systems alone are grouped as such.