How do I use HTML Agility Pack to edit an HTML snippet

Question

So I have an HTML snippet that I want to modify using C#.

<div>
This is a specialSearchWord that I want to link to
<img src="anImage.jpg" />
<a href="foo.htm">A hyperlink</a>
Some more text and that specialSearchWord again.
</div>

and I want to transform it to this:

<div>
This is a <a class="special" href="http://mysite.com/search/specialSearchWord">specialSearchWord</a> that I want to link to
<img src="anImage.jpg" />
<a href="foo.htm">A hyperlink</a>
Some more text and that <a class="special" href="http://mysite.com/search/specialSearchWord">specialSearchWord</a> again.
</div>

I'm going to use HTML Agility Pack based on the many recommendations here, but I don't know where I'm going. In particular,

1. How do I load a partial snippet as a string, instead of a full HTML document?
2. How do edit?
3. How do I then return the text string of the edited object?

Answer 1

1. The same as a full HTML document. It doesn't matter.
2. The are 2 options: you may edit InnerHtml property directly (or Text on text nodes) or modifying the dom tree by using e.g. AppendChild, PrependChild etc.
3. You may use HtmlDocument.DocumentNode.OuterHtml property or use HtmlDocument.Save method (personally I prefer the second option).

As to parsing, I select the text nodes which contain the search term inside your div, and then just use string.Replace method to replace it:

var doc = new HtmlDocument();
doc.LoadHtml(html);
var textNodes = doc.DocumentNode.SelectNodes("/div/text()[contains(.,'specialSearchWord')]");
if (textNodes != null)
    foreach (HtmlTextNode node in textNodes)
        node.Text = node.Text.Replace("specialSearchWord", "<a class='special' href='http://mysite.com/search/specialSearchWord'>specialSearchWord</a>");

And saving the result to a string:

string result = null;
using (StringWriter writer = new StringWriter())
{
    doc.Save(writer);
    result = writer.ToString();
}