Bundles
A bundle is a variant defined as a recipe: a list of component variants, each with a quantity. A single tube of tennis balls might be the stock-bearing variant, while a "box of 18" and a "deal of 3 tubes" are both bundle variants built from it — each with one component row of its own.
What happens when a bundle is ordered
When a bundle is added to an order, Yessort adds its components to the order behind the scenes — one line per component, at the recipe quantity multiplied by the quantity of the bundle ordered. Order two "deal of 3 tubes" bundles and Yessort adds a component line for six tubes.
The bundle line is the parent
The bundle line itself becomes the parent line — this is what's meant by the bundle parent. It carries no price of its own on the component lines, and it isn't dispatched as a thing in its own right. The components are what get reserved, allocated, routed to a pick and picked; the bundle line only carries the bundle's own selling price and quantity.
Changing quantity cascades to the components
Changing the quantity on the bundle line rescales every component line by the ratio the components were placed at — the ratio the recipe had when the bundle was added to the order, not whatever the recipe has been changed to since. A component's quantity is never rescaled below what's already been dispatched for it.
Returns go against the bundle line
A return is taken against the bundle line, not its components, and is worked out from the components actually dispatched. See customer returns for what happens once a return is open.
Bundles are single level
A bundle cannot contain another bundle. If you try to add a component that is itself a bundle, Yessort refuses it.
To set one up, see build a bundle.