jquery级联菜单遇到的问题，有段代码看不懂，求助……

<script type="text/javascript">  
        $(function() {              
            $("#selPro").change(function() {    //省份下拉菜单的change事件                  
                //var params = 'str:"' + $(this).val() + '"';  //此处参数名要注意和后台方法参数名要一致    
var urld = "?m=task&c=TaskManage&a=showTemplate&str=" + $(this).val();
                $.ajax({                      
                    type: "POST",                   //提交方式                      
                    url: urld,   //提交的页面/方法名                      
                    data: null,                   //参数（如果没有参数：null）                      
                    dataType: "text",               //类型                      
                    contentType: "application/json; charset=utf-8",                      
                    beforeSend: function(XMLHttpRequest) {                          
                        $('#tipsDiv').text("正在查询...");                      
                    },
                    success: function(msg) {                                                  
                        $('#tipsDiv').text("查询成功!");                         
                        $("#selCity option").each(function() {                              
                            $(this).remove();   //移除原有项                          
                        });                          
                        $("<option value='0'>请选择模板文件</option>").appendTo("#selCity");   //添加一个默认项                      
                        $(eval("(" + msg + ")").d).appendTo("#selCity");        //将返回来的项添加到下拉菜单中                      
                    },                      
                    error: function(xhr, msg, e) {                          
                        alert("error");                      
                    }                  
                 });              
            });         
        });      
        </script>  不明白的地方：$(eval("(" + msg + ")").d).appendTo("#selCity");        //将返回来的项添加到下拉菜单中$(eval("(" + msg + ")").d)这是什么意思？？？