Design custom documents using container panels. As they are added to panels, components are anchored to one panel edge. Using Slack alignment, you can realign objects to occupy all empty space.
Components placed with absolute alignment in the main document panel maintain their position as other components fluctuate. This may cause overlapping and shifting components. To prevent this, subdivide custom document space using panels, and anchor these panels to the master panel. Subsequently added components in container panels maintain their arrangement.