title: Regular expression to validate FQDN
body: <p>I am trying to use following Regular Expression to validate FQDN in Javascript. This works fine in C#. But Page throws 403 error when used in javascript. What am i doing wrong?</p>
  
  <pre><code> if (!fqdn.match(/(?=^.{1,254}$)(^(?:(?!\d|-)[a-zA-Z0-9\-]{1,63}(?&lt;!-)\.?)+(?:[a-zA-Z]{2,})$)/)) 
      {
          alert("Not a valid FQDN");               
          return false;           
      }
  </code></pre>