title: Behaviour of withCredentials flag of XMLHttpRequest lvl 2 in browser
body: <p>i'm trying to set a cookie in a XMLHttpRequest in a CORS environment, i receive the cookie in the last call to my server (developed with Restlet) in the Set-Cookie Header. As i can't read this header i have to leave the control to the browser (Chrome in this case), all the request to the server have to include the same value in the Cookie Header (the receive cookie in the first request). 
  I have to put the withCredentials (and set the allow-credentials header in the server) in the xhr request in the first call? this flag will take the Set-Cookie and put in the next xhr request on the Cookie header?</p>
  
  <p>Can someone clarify the behaviour of withCredentials flag in the browser? and other issue, in cors can i access to the document.cookie to set it? (will be the same if i can setRequestHeader("Cookie", value))????</p>