This read-create value selects an additional modifier, notApplicable, exact, additive, or communityNone, applied alongside the main match/set clause type for a route-map clause, defaulting to notApplicable. An admin sets it, for clause types like setCommunity that support it, to control whether new values replace or are added to existing ones. For example, setting this to additive(2) on a setCommunity clause appends the new community values to the route's existing community list instead of replacing it.