Decrease by one the (signed) length of the sequence of objects managed by this range proctor. The behavior is undefined unless the origin of the sequence of objects managed by this proctor is non‐zero. The behavior is undefined unless the origin or this range proctor is non‐zero. Note that if the length of this proctor is currently positive, the number of managed objects will decrease by one, whereas if the length is non‐positive, the number of managed objects will increase by one.