UML 2 allows to use some of the activity diagram’s symbols in statechart diagrams, in particular “actions”, “signal sending” and “signal receipt” to best specify transitions.
For an exmaple see fig. 15.44 (attached) from “UML 2.1.1 Superstructure specification”.
Although in VP-UML it is possible to place a activity diagram’s symbol (such as “signal sending”) on a state machine diagram, it is not possible to connect it to a state with a transition.
This would be a very useful feature.