You can add a superclass to a class in two ways: using the Superclasses pane or by drag-and-drop in the Class Relationship pane.
To add a superclass using the Superclasses pane:
To add a superclass using drag-and-drop in the Class Relationship pane:
Note that if you do not hold down the Ctrl key when releasing the mouse, the operation is interpreted as Replacing a Superclass.
If nothing happens when the class is dropped over a new superclass, the target class cannot be a superclass of the dragged class. For example, descendents of the dragged class are excluded.
Adding a superclass results in more than one superclass for a class, which then
inherits the slots and facets of all of its superclasses. In the Class
Relationship pane, a class with multiple superclasses is marked with
and has multiple occurrences, one for each superclass. For example, the Columnist
class in the Newspaper example has two occurrences in the Class
Relationship pane: one with the superclass Author, and one with the superclass
Person.
For information on replacing a superclass with a different superclass, see Replacing a Superclass.