The node template uses a custom Part.selectionAdornmentTemplate to add a row of Buttons when the node is selected. Select a node and you will see the Buttons for the node.
The first button, "T", when clicked, starts in-place editing of the text.
The second button, "C", when clicked, changes the color of the node, rotating through a list of colors.
The third button, "L", when clicked or dragged, starts the LinkingTool, drawing a new link starting at the selected node.
The fourth button, "N", when clicked, adds a new node and creates a link from the selected node to the new node. Dragging from the fourth button does the same thing as a click but also activates the DraggingTool, allowing the user to drag the new node where they like.
GoJS defines several Panels for common uses. These include "Button", "TreeExpanderButton", "SubGraphExpanderButton", "PanelExpanderButton", "ContextMenuButton", and "CheckBoxButton". "ContextMenuButton"s are typically used inside of "ContextMenu" Panels; "CheckBoxButton"s are used in the implementation of "CheckBox" Panels.
These predefined panels can be used as if they were Panel-derived classes in calls to GraphObject.make. They are implemented as simple visual trees of GraphObjects in Panels, with pre-set properties and event handlers.
More information can be found in the GoJS Intro.
The GoJS Geometry class controls the "shape" of a Shape, whereas the Shape.fill and Shape.stroke and other shape properties control the colors and appearance of the shape. For common shape figures, there are predefined geometries that can be used by setting Shape.figure. However one can also define custom geometries.
One can construct any Geometry by allocating and initializing a Geometry of at least one PathFigure holding some PathSegments. But you may find that using the string representation of a Geometry is easier to write and save in a database. Use the static method Geometry.parse or the Shape.geometryString property to transform a geometry path string into a Geometry object.
More information can be found in the GoJS Intro.