P.S. I'm now looking at the very first paragraph to initdb more closely, not liking "single server instance" all that much and wondering how to fit in "cluster user" there - possibly by saying something like "...managed by a single server process, and physical data directory, whose effective user and owner respectively is called the cluster user. That user must exist and be used to execute this program."
Then the whole "initdb must be run as..." paragraph can probably just go away. Moving the commentary about "root", again a non-Windows thing, to the notes area.
Version 2 attached, some significant re-working. Starting to think that initdb isn't the place for some of this content - in particular the stuff I'm deciding to move down to the Notes section. Might consider moving some of it to the Server Setup and Operation chapter 19 - Creating Cluster (or nearby...) [1].
I settled on "cluster owner" over "cluster user" and made the terminology consistent throughout initdb and the glossary (haven't looked at chapter 19 yet). Also added it to the glossary.
Moved quite a bit of material to notes from the description and options and expanded upon what had already been said based upon various discussions I've been part of on the mailing lists.
Decided to call out, in the glossary, the effective equivalence of database superuser and cluster owner. Which acts as an explanation as to why root is prohibited to be a cluster owner.
