A display perimeter written without its own tag reloaded as an ordinary
cut, so a saved blank would come back with its outline to be cut. Programs
now carry it as :DISPLAYPERIMETER and the reader maps it back, and stored
source entities keep the DISPLAY PERIMETER layer so editing the drawing
rebuilds the same never-cut outline.
Builds older than this read the unknown tag as a cut. Open nests with
display perimeters only in builds that include this change.