How to parse doctype to string as html doctype

I'm working on C# app to get html file from current IE tab by EnumWindows. Now I got HTMLDocument and can parse it to html file from outerHTML ({HTMLDocument}.documentElement.outerHTML) by HtmlAgilityPack, but my output html file has not doctype.

I see that HTMLDocument has doctype property, how can I parse it to string as same as tag in html file

Solution

I got it by casting htmlDocument.doctype as dynamic object. Another, you can get other tags which are out of <html> tag by looping on (dynamic)htmlDocument.childNodes list

private static void InsertDocType(HTMLDocument htmlDocument, HtmlDocument document)
{
    // get html node
    HtmlNode htmlNode = document.DocumentNode.SelectSingleNode("/html");

    // get doctype node from HTMLDocument
    var doctype = (dynamic)htmlDocument.doctype;

    StringBuilder doctypeText = new StringBuilder();
    doctypeText.Append("<!DOCTYPE");
    doctypeText.Append(" ");
    doctypeText.Append(doctype.name);

    // add PUBLIC
    if (!string.IsNullOrEmpty(doctype.publicId))
    {
        doctypeText.Append(" PUBLIC \"");
        doctypeText.Append(doctype.publicId);
        doctypeText.Append("\"");
    }

    // add sytem id
    if (!string.IsNullOrEmpty(doctype.systemId))
    {
        doctypeText.Append(" \"");
        doctypeText.Append(doctype.systemId);
        doctypeText.Append("\"");
    }

    // add close tag
    doctypeText.Append(">");
    doctypeText.Append(Environment.NewLine);

    HtmlCommentNode doctypeNode = document.CreateComment(doctypeText.ToString());
    document.DocumentNode.InsertBefore(doctypeNode, htmlNode);
}