(i) If an item is one of the standard objects in the main NDF and the effect of the program on that object is completely known then propagate.
(ii) If an item becomes invalid after an operation, then a warning message should be output and the item should not be propagated.
(iii) If an item is in the MORE extension then it should be propagated by default. If a particular application 'knows' that an extension item has been invalidated then rule (ii) applies.
(iv) If a non-standard item is found in the main NDF it should not be propagated.