Question about Krenov cabinets

Solid wood frame and panel. It’s described in of the books.

Thanks. So if the bottom and top are simple boards doweled to the sides, the back as a whole will move front to back with them, no problem. When I look at the cabinet in the middle here:

http://jameskrenov.com/furniture.htm

I wonder how the box is attached, surely not to the tops of the legs? Or is there some sliding system on top of the legs, like buttons in principle? A number of his “vintage television set” style cabinets have me scratching my head as to how he made them without cross grain problems.

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.