Chapter 13 of the documentation on Rules versus Triggers says in part
"On the other hand a trigger that is fired on INSERT on a view can do the same as a rule, put the data somewhere else and suppress the insert in the view."
However, it does not appear to be possible to set a trigger on a view, so this means something else. (I'd like to set a trigger on a view, because the replacement INSERT I wish to make is easier to write in PLPGSQL than plain SQL.)