title: How set HTTP *Request* header programmatically (e.g. by <a> -tag, <link> -tag, or by JavaScript)?
body: <p>This question is about HTTP <em>Request</em> headers -- not HTTP Response headers.</p>
  
  <p>Is there any way to programmatically make User Agents add or change any HTTP Request Header e.g. by means of HTML, JavaScript, for links or resources from a web page. There exists some HTTP Request Headers that one would think should be able to be controlled programmatically, for example <code>max-stale</code>.</p>
  
  <p>(One could for example imagine that some optional attribute for HTML-elements <code>&lt;a&gt;</code>, <code>&lt;link&gt;</code>, <code>&lt;img&gt;</code> <code>&lt;script&gt;</code> etc, could exist that would cause the User Agent to add/change a HTTP request header in its request to the server, but I have not found such an attribute. Similarly, one could think that there should exist some mechanism to control HTTP Request Headers when AJAX is used.)</p>
  
  <p>Turning around the question ...: Why does the HTTP Request Header <code>max-stale</code> exist at all if it cannot be controlled?</p>
  
  <p>Thanks!</p>