jquery ajax调用php方法

jquery ajax方法:

   jQuery.ajax({   type: "POST",   url: "/v_ajax.php",   data: "action=getUmsg&u="+winduid,   success: function(r_msg){                            var flag = jQuery(r_msg).find("flag").text();});

?php端返回:

?? ??? header('Content-Type: text/xml');
??? echo "<?xml version='1.0' encoding='gbk'?>";
??? echo "<response>";
??? echo "<flag>true</falg>";
??? echo "</response>";