When in The Void, the entrances are not automatically opened if the room is not yet cleared. Re-entering the room once enemies are killed and/or Pressure Plates pressed will open the doors normally.
When Book of Secrets is used while all mapping effects have been obtained, trough book of secrets itself or another mapping effect, the X-Ray Vision effect is given.
The flavor text "I've seen everything" could be a reference to Patrick Stewart's popular scene in the TV series "Extras".
The cosmetic is a reference to 'X-ray Specs' sold as gag-gifts or on the back of Comic books in the 1960's and 70's.
Secret Rooms and 
Super Secret Rooms automatically.
When in 
The Void, the entrances are not automatically opened if the room is not yet cleared. Re-entering the room once enemies are killed and/or 
Pressure Plates pressed will open the doors normally.
When 
Book of Secrets is used while all mapping effects have been obtained, trough book of secrets itself or another mapping effect, the X-Ray Vision effect is given.
The Binding of Isaac: Rebirth
