code: function focusable(element) {
  		// Use the defined focusable checker when possible
  		if($.expr[':'].focusable) { return $.expr[':'].focusable; }
  
  		var isTabIndexNotNaN = !isNaN($.attr(element, 'tabindex')),
  			nodeName = element.nodeName && element.nodeName.toLowerCase(),
  			map, mapName, img;
  
  		if('area' === nodeName) {
  			map = element.parentNode;
  			mapName = map.name;
  			if(!element.href || !mapName || map.nodeName.toLowerCase() !== 'map') {
  				return false;
  			}
  			img = $('img[usemap=#' + mapName + ']')[0];
  			return !!img && img.is(':visible');
  		}
  
  		return /input|select|textarea|button|object/.test( nodeName ) ?
  			!element.disabled :
  			'a' === nodeName ?
  				element.href || isTabIndexNotNaN :
  				isTabIndexNotNaN
  		;
  	}
docs: Modified code from jQuery UI 1.10.0 source http://code.jquery.com/ui/1.10.0/jquery-ui.js