title: Why is System.TimeSpan not XML serializable?
body: <p>When I try to store a TimeSpan value into ApplicationData Settings I get an error because TimeSpan cannot be serialized. This SO question shows how to handle it: <a href="https://stackoverflow.com/questions/637933/net-how-to-serialize-a-timespan-to-xml">How to serialize a TimeSpan to XML</a></p>
  
  <p>Why is it that TimeSpan would not be easily serializable? </p>
  
  <p>And, is there a list of data types that cannot be serialized?</p>