I wanted to share a document and like the ten ox pictures, a way with different steps, by one of the founder of the soto zen.
Remember, those ranks are not an intellectual study, nor a method, but different phases wherein we go through the experiment of shikantaza as well in sitting and in daily life.
The theory of Tozan is associated with some verses on this link
After that, we can also see the application with the Genjokoan, where Dogen describes all those ranks without mention of the names.
I let you discover with scholars peoples, I'm not able not explain you and that's not my aim.