title: Validation spanning a group of text boxes
body: <p>I'm trying to achieve the following:
  <img src="https://i.stack.imgur.com/wf52L.jpg" alt="enter image description here"></p>
  
  <p>Where:</p>
  
  <ul>
  <li>Surname is always required</li>
  <li>NI Number OR Reference Number is required</li>
  </ul>
  
  <p>Is this beyond the scope of the <a href="http://msdn.microsoft.com/en-us/library/aa479013.aspx" rel="nofollow noreferrer">ASP.NET Validation Controls</a>?  The only solution I can think of is writing some bespoke javascript (for client side) and backing that up with some server side code.</p>