That pseudocode sequence helps a lot. It also confirms that the meaning of the levels, essentially, is a "skip this under what conditions" setting, where none gets you constant reading (skip none), and, under typical NVDA settings conditions, all gets you never read (skip all).
When I first started looking at this I was interpreting the level as a "speak under what conditions" descriptor, taking "all" as meaning speak always and none as meaning "don't ever speak it."
For me, it seemed that some of the descriptions during this exchange were each saying the above (though only one of the above). This is also not documented well anywhere that I can find, which made things worse. I realize that these sorts of "under the hood" level functions are seldom twiddled, but that makes documentation regarding same even more essential for when someone actually wants or needs to twiddle.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
~ Saul Bellow, To Jerusalem and Back