docs: function() {
              var queue = [this];
              var i, node;
              for (var i = 0; i < queue.length; i++) {
                  node = queue[i];
                  if(node.plane) node.plane = node.plane.flipped();
                  if(node.front) queue.push(node.front);
                  if(node.back) queue.push(node.back);
                  var temp = node.front;
                  node.front = node.back;
                  node.back = temp;
              }
          }