This interface should be implemented in order to receive border crossing warnings for country and state borders. Note: The border crossing warner is a point warner, which means that for a border crossing there will always be 2 warnings emitted, with the [BorderCrossingWarning.distance_type] set to DistanceType.AHEAD and DistanceType.PASSED which is given when the location of the border crossing is reached. A BorderCrossingWarning will not be given until the previous warning of that type has been passed. For example, a route with BorderCrossingWarning 120 meters and BorderCrossingWarning 160 meters ahead, the first [BorderCrossingWarning.distance_to_border_crossing_in_meters] is 120 meters and the next [BorderCrossingWarning.distance_to_border_crossing_in_meters] is then 40 meters, since that is the distance between the first and second warnings.