title: xml.setRequestHeader fails with SYNTAX_ERR: DOM Exception 12
body: <p>I am trying the following code:</p>
  
  <pre><code>    // create a request
      var xml = new XMLHttpRequest();
      xml.open("GET", url, false);
      xml.setRequestHeader("Authorization", "Negotiate " + base64Token);
  </code></pre>
  
  <p>and it fails at the last line (setRequestHeader) with the error: </p>
  
  <blockquote>
    <p>SYNTAX_ERR: DOM Exception 12</p>
  </blockquote>
  
  <p>I've tried debugging it but not entirely sure why this is happening! I am opening the request before setting the header and I haven't sent it yet.</p>
  
  <p>I am currently testing this on Chrome 21</p>
  
  <p>Any help is appreciated!</p>