title: xcb keyboard button masks meaning
body: <p>I'm trying to figure what keys are handled by:</p>
  
  <ul>
  <li>XCB_MOD_MASK_1</li>
  <li>XCB_MOD_MASK_2</li>
  <li>XCB_MOD_MASK_3</li>
  <li>XCB_MOD_MASK_4</li>
  <li>XCB_MOD_MASK_5</li>
  </ul>
  
  <p>in xcb, for XCB_MOD_MASK_1 it seems to be Alt (i'm correct?), but for others button i cannot find the mapping anywhere (i tried to google them before posting, but with no success). </p>
  
  <p>So what are the usual key associated to these masks?</p>