Is it allowed to instal curtains on the rear windows of the vehicle?

Explanation
The windows of the vehicle must always allow the driver a proper visibility of the entire road on which it circulates, without interference from films or stickers.
Only when the vehicle is equipped with two exterior rear-view mirrors, one on each side, that meet the necessary technical specifications will it be allowed to drive with such adhesive films or sun blinds on the rear windows.
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