code: function( elem, classNames ) {
  			jQuery.each((classNames || "").split(/\s+/), function(i, className){
  				if ( elem.nodeType == 1 && !jQuery.className.has( elem.className, className ) )
  					elem.className += (elem.className ? " " : "") + className;
  			});
  		}
docs: internal only, use addClass("class")