Each node has a "Flow" PanelLayout below the shape listing a bunch of text values in rows.
The context menu shown for each node has three "tabs", each showing some number of shape figures, one of which the user can click to replace the node's shape's figure. These tab panels use a "Flow" PanelLayout to arrange the shapes in columns, by setting PanelLayoutFlow.direction to 90. Note how for a custom PanelLayout one cannot use its name directly, but must construct and initialize an instance of the PanelLayout.
This extension is defined in its own file, as PanelLayoutFlow.js.