the example of Loan
replace constructors with Creation Method
replace conditions with Strategy
Polymorphism to replace conditions
example of OrdersWriter(XML)
Compose Method
drive out TagNode and replace the most leaf node at first
completely replace hidden tree with Composite-TagNode
Drive out TagBuilder for TagNode.
Can add child and sibling by remembering parentNode.
handle TagBuilder.addToParent()
completely wrap all TagNode with TagBuilder