Option 4:  If a linking match is found…
On Enter:  DELETE the target record.
On Replace:  CREATE a new target record, then DELETE a 
  target record.
On Delete:  MODIFY Fields in the target record. If no
  match is found, CREATE a new record.

Option 3:
On Enter/Replace:
  If a linking match is found, MODIFY Fields in the target
  record. If no match is found, CREATE a new target
  record.
On Delete:
  If a linking match is found, DELETE the target record.

Option 2:
On Enter/Replace or Delete:
  If a linking match is found, MODIFY Fields in the target
  record. If no match is found, CREATE a new record.

Option 1:
On Enter/Replace or Delete:
  If a linking match is found, MODIFY Fields in the target
  record.

Option 0:
On Enter/Replace or Delete: MODIFY Fields in the current record.
  This only modifies Fields that are either not selectable on the current form.