code: function focusable( element, isTabIndexNotNaN ) {
  	var map, mapName, img,
  		nodeName = element.nodeName.toLowerCase();
  	if ( "area" === nodeName ) {
  		map = element.parentNode;
  		mapName = map.name;
  		if ( !element.href || !mapName || map.nodeName.toLowerCase() !== "map" ) {
  			return false;
  		}
  		img = $( "img[usemap='#" + mapName + "']" )[ 0 ];
  		return !!img && visible( img );
  	}
  	return ( /^(input|select|textarea|button|object)$/.test( nodeName ) ?
  		!element.disabled :
  		"a" === nodeName ?
  			element.href || isTabIndexNotNaN :
  			isTabIndexNotNaN) &&
  		// the element and all of its ancestors must be visible
  		visible( element );
  }
docs: selectors