Increase by one the (signed) length of the sequence of memory blocks managed by this range proctor. The behavior is undefined unless the origin of the sequence of memory blocks 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 negative, the number of managed memory blocks will decrease by one, whereas if the length is non‐negative, the number of managed memory blocks will increase by one.