The glyph start marker ╵ also marks a block of code; if several consecutive glyphs start with the same number of them, they are part of the same block.

When the question strand executes, it looks at whether a list element (or entire list) is zero or below. If so, the entire block is rolled back to its previous state.

So all branching is done as rollbacks. And loops end by rolling back their last iteration.