"in" or "within" attribute

JQuery UI positions could be enhanced with an "in" or "within" attribute.

This attribute would augment the existing keywords to allow positioning to a specific item (my) within a container (within).

The typical windowed slider could easily be positioned as

#!text/html
<div id="window">
  <ul id="slider">
    <li>Item 1</li>
    <li class="selected">Item 2</li>
    <li>Item 3</li>
  </ul>
</div>

<script>
$('#slider .selected').position({
  my:'center top',
  at:'center top',
  of: $('#window'),
  within: $('#slider')
})
</script>