All items in the diagram document - links and nodes - share common base class called DiagramItem. Its main function is to provide interface for the most common methods and properties of every diagram element.
The main textual content of an item is set using the text property. Supplementary labels can be created by calling addLabel.
Appearance can be customized using a shared Style object assigned to the style property. Attributes of the shared style can be overridden by setting item's properties such as brush, stroke, font.