Custom Doubly Linked List Implementation

Question

Given the following code snippet, I need clarification on a Custom Doubly Linked List Implementation:-

I have placed comments under each line of code, please correct where necessary...

  public void ReverseList()

        {

            CustomDoubleLinkedListItem<T> node = this.RootNode.NextNode;

      // Get a reference to the current root nodes next node? what is this previously set to and how, constructor?

            CustomDoubleLinkedListItem<T> previousNode;

// declare a field named previous node

            CustomDoubleLinkedListItem<T> nextNode;

// declare a field named next node

            while (node != null)

            {

                nextNode = node.PreviousNode;

// next node is set to reference the nodes previous node

                previousNode = node.NextNode;

// previous node is set to reference the nodes next node

                node.PreviousNode = previousNode;

// the nodes previous node is set to reference the previous node

                node.NextNode = nextNode;

// the nodes next node is set to reference the next node

                //Handle the old root? what is meant by old root?

                if (previousNode == null)

                {

                    previousNode = this.RootNode.NextNode;

   // previous node is set to reference the current root nodes next node

                    

this.RootNode.NextNode = null;

   // current root nodes next node is set to reference null        

                

       this.RootNode.PreviousNode = previousNode;

   // set the root nodes previous node to reference the previous node

                    

this.RootNode = node; 

   // set the current root node to reference the node, which node? old or current?

                

    previousNode = null;

                }

                if (previousNode == this.RootNode)

                {

                    node.PreviousNode = null;

                }

                node = previousNode;

            }       

// Not sure the whole logic of the above comparsion\equality?     

        }

Thanks