Changing an element's optionality from optional to required is related to refinement for those optional elements that are not instantiated on the original document.
As I discuss later in this article, two areas that often require particular attention are cardinality and optionality, or conformance strength.
With the background of market-oriented interest rate, housing mortgage loans have to face enormous interest rate risks in forms of repricing, optionality, basic risk, and yield curve.