ChildSeparatorMove Event
The ChildSeparatorMove event provides information about the new position of a StackField separator when the SeparatorMoving attribute of a StackField is either SM_MANUAL or SM_RESIZE and the user drags and releases a separator.
on childseparatormove [compositefield]
compositefieldname is optional if you specify the event in a field script for a composite field, or if the composite field is the frame's top form.