The Notepad is a canvas which displays items. An item is given by the class CItem; it has a name and an icon. The notepad lets the user arrange the icons by dragging them around, and allows drag-and-drop between items.
The generic GenGUI interface allows the visualisation of items which are arranged in a hierarchical structure. It uses a tree list to display the hierarchy, a notepad to display all items, and an editor to display a single item selectable by double-clicking. See the examples in htk/examples/gengui.