In this design each swimlane is implemented by a Group, and all lanes are inside a "Pool" Group. Each lane Group has its own Group.layout, which in this case is a LayeredDigraphLayout. Each pool Group has its own custom GridLayout that arranges all of its lanes in a vertical stack. That custom layout makes sure all of the pool's lanes have the same length.
When dragging nodes note that the nodes are limited to stay within the lanes. This is implemented by a custom Part.dragComputation function, here named stayInGroup. Hold down the Shift key while dragging simple nodes to move the selection to another lane. Lane groups cannot be moved between pool groups.
A Group (i.e. swimlane) is movable but not copyable. When the user moves a lane up or down the lanes automatically re-order. You can prevent lanes from being moved and thus re-ordered by setting Group.movable to false.
Each Group is collapsible. The previous breadth of that lane is saved in the _savedBreadth property, to be restored when expanded.
When a Group/lane is selected, its custom Part.resizeAdornmentTemplate gives it a broad resize handle at the bottom of the Group and a broad resize handle at the right side of the Group. This allows the user to resize the "breadth" of the selected lane as well as the "length" of all of the lanes. However, the custom ResizingTool prevents the lane from being too narrow to hold the Group.placeholder that represents the subgraph, and it prevents the lane from being too short to hold any of the contents of the lanes. Each Group/lane is also has a GraphObject.minSize to keep it from being too narrow even if there are no member Parts at all.
A different sample has its swim lanes vertically oriented: Swim Lanes (vertical).Diagram Model saved in JSON format: