docs: function(){
              if(!this.size) return;
              var n = this.root, pr = n.previous, nx = n.next;
              if(this.size === 1){
                  this.root = this.tail = null; this.size = 0;
                  return n;
              } 
              nx.previous = pr; 
              delete this.root;
              this.root = nx;
              this.size -= 1;
              return n;
            }