PD_ZONE_ADD command
+------------+
| |
-->(PD_ZONE_ADD)--+---------------+--v--|select|--^-->
| |
+--(NEIGHBORS)--+
PD_ZONE_ADD adds elements to the modify zone. If the NEIGHBORS qualifier is not given, then the elements added are the elements selected. If the NEIGHBORS qualifier is given then the elements added to the zone are the elements selected and any elements that share a model point with one of the elements selected.
The modify zone is the set of elements which might be modified by the PD_RESOLVE command.