title: How HttpNotFound is implemented and how to create similar methods for other errors?
body: <p>In ASP.NET MVC, <code>Controller</code> class has only a limited set of methods to use to return something from an action.</p>
  
  <p>There is a <code>HttpNotFoundResult HttpNotFound()</code> method, but no other methods for errors.</p>
  
  <p>What's really inside <code>HttpNotFound()</code>? How to write a similar method for other error codes, like <code>401 Unauthorized</code> or <code>403 Forbidden</code> or <code>406 Not Acceptable</code>?</p>