How do branch inheritance and releasing changes work in 7.2 Solution Documentation?

Beyond production+maintenance you can add project branches/sub-branches (e.g. a dev track for the next major release).

A branch always contains its parent's content, and an element has the same identity across all branches — so a change released to production becomes visible automatically in all child branches. Release via right-click → Release Changes (Element Changes = this node only; Subtree Changes = all children).