title: What is the purpose of HttpHeaders.TryAddWithoutValidation?
body: <p>In the System.Net.Http.Headers namespace, what is the difference between <a href="http://msdn.microsoft.com/en-us/library/hh875107.aspx" rel="noreferrer">HttpHeaders.TryAddWithoutValidation</a> and <a href="http://msdn.microsoft.com/en-us/library/hh158900.aspx" rel="noreferrer">HttpHeaders.Add</a>? </p>
  
  <p>Specifically, what validation is occurring when calling the Add method? The documentation for Add() simply states: </p>
  
  <blockquote>
    <p>"The header value will be parsed and validated."</p>
  </blockquote>