Does the plate under this sign indicate the layout of non-priority roads?

Why?

Below the D-1 priority-road sign is a T-6b supplementary plate showing the layout of roads that must give way. The thick line represents the priority road, while the thin branches on the right represent the minor roads.

§ 43 ust. 2 rozporządzenia w sprawie znaków i sygnałów drogowych, tabliczka T-6b