Returns the head element of the structure.
Returns the head element of the structure. Note that this is O(n) worst case.
The initial element created from which you can start to append and prepend.
The number of elements in the order.
The number of elements in the order. This is 1
for a newly
created order (consisting only of the root element).
You will rarely need this information except for debugging
purpose. The operation is O(1).