Regions can be created in Composite States or State Machines on a State Machine diagram. Regions indicate concurrency, such that a single State is active in each region. Multiple transitions can occur from a single event dispatch, so long as similarly triggered transitions are divided by Regions.

To create a Region in a Composite State or State Machine element, follow the steps below:

  1. Right-click on the element, and select the Advanced | Define Concurrent Substates context menu option. The State Regions dialog displays.
  2. Create the Regions of a State, which can be named or anonymous.
  3. Click on the OK button.

OMG UML Specification

The OMG UML specification (UML Superstructure Specification, v2.1.1, p. 544) states:

A region is an orthogonal part of either a composite state or a state machine. It contains states and transitions.