I thought I'd post an update given the many questions on this topic. I'm the bottleneck on documentation, something that wasn't supposed to happen, but...stuff happened. No need to rehash that.
There are three major documents in the works:
1. K4 Built-In Operating Manual
This is an .html document normally viewed on the K4's LCD or external monitor. You get to it by tapping the button labeled "?" in the lower-left-hand corner of the LCD.
For review purposes the doc can be viewed in any browser. And in fact, late next week we'll be looking for a few hardy volunteers who don't mind going through 60 pages of text, trying every link.
In the radio context, the operating manual is supplemented by direct hyperlinks attached to every control and menu entry. There's a "LAST CONTROL" button that takes you directly to text most closely associated with the last operation performed.
2. K4 Owner's Manual
Because of its multitude of full-color illustrations, the owner's manual will be 150-200 pages when finished. It'll be a fully searchable and indexed .pdf file, and two steps up from our earlier manuals. Early K4 users have been using a much smaller document that has many of the same illustrations.
The built-in operating manual provides the framework for the owner's manual, so I expect rapid progress on the latter as soon as the former is blessed.
3. K4 Programmer's Reference
An early draft of this doc has been in use by a our team and by a few developers who have been vetting it for us. Many of the apps available for the K3/K3S are already working with the K4 in emulation mode. But we're trying to expedite the public version of the reference so developers can take advantage of all of the new features.