How it works
Take a rectangle, cut it in two, and do the same to both halves until something says stop. That is the whole algorithm, and it is here because it is the only piece in the set whose output is a hierarchy rather than a field or a path. Every leaf knows how deep it is, and the recursion nests strictly, which is why the result reads as composed even though nothing composed it. Where a flow field gives you texture, this gives you layout.
Three decisions make all the difference and all three are controls. Which way to cut: across the longer side keeps every piece roughly square, while cutting a side at random makes slivers. Where along the side: dead centre gives graph paper, and the jitter is what stops it. And when to stop, which is a probability rather than a depth — that is what makes the sizes uneven. Early stopping is held back until the sheet has been cut a few times, because one unlucky roll at the top level otherwise leaves a third of the page as a single blank rectangle.
The gutter is taken off every piece rather than off every cut, so it compounds with depth: shallow pieces sit further apart than deep ones, and the hierarchy is legible in the spacing without anything drawing it. What goes inside a leaf — flat colour, hatching, nested rectangles, a dot grid — is decided per piece and is the only part of this that is decoration rather than structure.