One of my favorite Mac apps, DiskWarrior, has been waiting for the APFS format documentation (also called the APFS volume specification) for a while, in order to make a new program version which can rebuild APFS disks. Recently, according their page linked above, this documentation was released and Alsoft is using it to update DiskWarrior. I would like to look at this documentation myself, as I find it interesting. However, I can't find the documentation anywhere. I've found a few documents like this, but I don't think that's what I'm looking for, since that document is not as comprehensive as what I would expect from a full volume format specification.
Do I need a certain Apple subscription to see this documentation or am I simply failing at googling for it?