appcan frame open，引入的URL页面中的元素如何获取

var titHeight = 0,
content = 0;
var http,
user,
upwd,
hash_pwd,
AppID,
AppUserId,
AppTID;

    appcan.ready(function() {
        titHeight = $('#header').offset().height;
        content = $('#reply').offset().height;
        var url = "http://192.168.1.188/jc6/wfAndroidHtml/knowledge2.html?UserCode=xiaoyujie%24356a192b7913b04c54574d18c28d46e6395428ab&AppTID=ff8080814a98d7af014&AppID=10333&usr=xiaoyujie&pwd=356a192b7913b04c54574d18c28dflag=1&end=1";
        appcan.frame.open("content", url, 0, parseInt(titHeight) + parseInt(content));   

    });
            appcann中用URL引用远程页面，我想修改引用的红色页面的元素，涉及跨域问题，请问怎么写代码,尽量详细