Building a Simple RSS reader, retrieving content

I am trying to make a simple RSS reader using SyndicationFeed class.

There are some standard tags, like <title>, <link>, <description>... there is no problem with them.

But there are some other tags. for example, in this feed, which created by WordPress, there is <content:encoded> tag. I think there may be other tags for the content part of other websites. right?

I want to know, how to find the main content of every post, is there any standards? which tags should I look for?

(for example, a site may use <content:encoded> but some other just use <description> or someone use another standard... I don't know what to do for retrieving the main content of a post)

P.S : I'm using this code for testing my simple RSS reader:

        var reader = XmlReader.Create("http://feed.2barnamenevis.com/2barnamenevis");        var feed = SyndicationFeed.Load(reader);        string s = "";        foreach (SyndicationItem i in feed.Items)        {            s += i.Title.Text +"<br />"+ i.Summary.Text +"<br />"+ i.PublishDate.ToString() +"<br />";            foreach (SyndicationElementExtension extension in i.ElementExtensions)            {                XElement ele = extension.GetObject<XElement>();                s += ele.Name +" :: "+ ele.Value +"<br />";            }            s += "<hr />";        }        return s;