title: Is background-position-x (background-position-y) a standard W3C CSS property?
body: <p>I'm worried about <code>background-position-x</code> and <code>background-position-y</code>. Gecko (Firefox) and Presto (Opera) don't support them, but Webkit (Chrome, Safari) does...</p>
  
  <p>Does anyone know (with official references) if this is (or will be) included in the standard?</p>