How are UML elements created?
You can create UML2 elements under the UML top-level elements Package, Model, and Profile. This means that these must first be placed in a group in the database, so that UML2 elements can be made subordinate to them and thus created.
This also means that, apart from the UML top-level elements, no UML elements can be created in groups.
Exceptions are diagrams acting as a behavioral feature, e. g., the activity diagram as an activity or a sequence diagram as an interaction. These are not created directly below a top-level element, but below the behavior that is represented by the diagram.
If a behavior diagram is created using the pop-up menu, the corresponding behavioral feature is created within the top-level element first, and then the diagram is created below. The name of the diagram is applied to the behavior.