Below is from Cadence community:
How to set up a constraint region in 16.2.
Lets say we want to create a spacing region:
Open constraint manager and create a Spacing Rule set for the constraint region.
1. Open Constraint Manager on the board file.
2. Select Spacing > All Layers worksheet
3. RMB on the Objects and select Create Spacing CSet
4. Type the name of Spacing CSet and change the pin to pin constraints that allow
pin to pin spacing for the 'special' component.
Now create a region and assign a spacing CSet to the region.
1. In Constraint Manager, select Region > All Layers
2. RMB > Create Region
3. Give a name to the region, and select Ok.
4. On the Region worksheet, select the region that you just created, and assign
the Spacing CSet that you had created in the previous step. The rules of the
spacing CSet are automatically taken over by the Region.
Now create a Shape on Constraint Area subclass and assign the region rules to it.
1. On Allegro, Select Shape > Polygon or Rectangular.
2. In the Options panel on the Right hand side, select the Class as Constraint
Region > All.
3. From the drop down in the options panel, select the Region you had defined in
the previous step.
4. Draw the rectangle or polygon around the component.