6. The computer program product in accordance with claim 5 , wherein the act of determining that the model element should be changed comprises an act of detecting that a user has interfaced with the viewer with one or more gestures indicative of a user intent to perform the change.
6. The computer program product in accordance with claim 5 , wherein the act of determining that the model element should be changed comprises an act of detecting that a user has interfaced with the viewer with one or more gestures indicative of a user intent to perform the change. 7. The computer program product in accordance with claim 6 , wherein the one or more gestures do not include a separate gesture for deleting the model element of the first model element type and a separate gesture for adding the model element of the second model element type.