Palette extends the Diagram class to allow objects to be dragged and placed onto other Diagrams. Its Diagram.layout is a GridLayout. The Palette is Diagram.isReadOnly but to support drag-and-drop its Diagram.allowDragOut is true.
You can control the order of Parts in the palette in several manners:
myPalette.model.nodeDataArray, just set
myPalette.layout.sorting = go.GridLayout.Forward(GridLayout.sorting).
A reference to a div or its ID as a string.