title: Position a constrained Window relative from the center and top of the constraining container
body: <p>We need to position a constrained Window (like in this <a href="http://docs.sencha.com/extjs/4.2.2/#!/example/layout/border.html" rel="nofollow">example</a>) relative from the top and the center of the container where it is constrained to. But in the config we only found x and y which would require to calculate the center on each document change. </p>
  
  <p>Isn't there any other way to archive this?</p>