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The Villager Barrier Detector can disable and enable Villager Barriers by right clicking a barrier. In the disabled state Villagers can pass through the barrier blocks. Once the blocks are enabled again the blocks will stop Villagers from passing through.
Holding the Villager Barrier also allows the barriers to be seen.
This is what is seen without the Villager Barrier Detector or Villager Barrier items held in hand. There is no bounding box and no texture for the Villager Barrier block. The Villagers are still held back by the barrier.