Let us build as an example a circular inclusion between two plates. We will simply treat the plates as the top and bottom surfaces of a square enclosure, with the circle centered between them. Using the statements above and adding the required control labels, we get:
BOUNDARIES
REGION 1 'box' { the bounding box }
START(-1,-1)
LINE TO(1,-1)
TO (1,1)
TO (-1,1)
TO CLOSE
REGION 2 'blob' { the embedded circular 'blob' }
START 'ring' (1/2,0)
ARC(CENTER=0,0) ANGLE=360 TO CLOSE
The resulting figure displayed by the "domain" button is this:
[Note: The detailed Rules for constructing domain boundaries is included in the Reference chapter "Sections | Boundaries".]