code: function(q) {
           var list = xui(q);
           return this.filter(function () {
               var that = this;
               var found = null;
               list.each(function (el) {
                   found = (found || el == that);
               });
               return found;
           });
       }
docs: has
  ---
  
  Returns the elements that match a given CSS selector.
  
  ### syntax ###
  
  x$( window ).has( selector );
  
  ### arguments ###
  
  - selector `String` is a CSS selector that will match all children of the xui collection.
  
  ### example ###
  
  Given:
  
  <div>
  <div class="round">Item one</div>
  <div class="round">Item two</div>
  </div>
  
  We can use `has` to select specific objects:
  
  var divs    = x$('div');          // got all three divs.
  var rounded = divs.has('.round'); // got two divs with the class .round