title: Possible values for X-Requested-With header?
body: <p>The x-requested-with header is kind of confusing to me. I know it can be used to defend against CSRF attacks, and that it is used to identify Ajax calls...but what is it really?</p>
  
  <p>It just tells you what the request was...requested with?</p>
  
  <p>Could there ever be a reasonable situation in which the header is present but set to some value other than "XMLHttpRequest"? I would imagine so, but I've never seen it set to anything else. </p>