Set this property to true if this keyVariable, when not blank, is used differently than other keyFields on the same screen in terms of navigation.
For example, if a screen includes three possible search arguments, each one a keyVariable field, but all are used in the same fashion to perform a search, arriving at the same screen(s), then each of these keyVariable fields would have the UniqueNavigation property set false (the default value).
On the other hand, if of the different search arguments, one of them, when not blank, triggers a completely different type of search, with unique screens resulting, then it would have UniqueNavigation set true.
