TOGGLE_RELATION activates/de-activates a Relation within the
active Relation Set.
+-----------------<----------------+
| |
--->(TOGGLE_RELATION)--+--------|select Relations|--------+-->
This action has no options.
Use this action to de-activate an active Relation, or activate a
de-activated Relation, within the active Relation Set.
The following parameter sequence de-activates an active Relation.
TOGGLE_RELATION [select Relation] COMPLETE
SET_CURRENT_REL_SET terminate action