A complex transition may have multiple source states and target states. It represents a synchronization and/or splitting of control into concurrent threads.

A complex transition is enabled when all of the source states are occupied. After a complex transition fires all of its destination states are occupied.

The complex transition is represented by a Synchronization Bar, which is a short heavy bar that has one or more solid transition arrows drawn from "source" states to the bar, and one or more solid transition arrows drawn from the bar to "destination" states.