如何使用HTML Agility Pack向表单添加输入标记？

Question

I start off with a set of forms:

<form action="/Test/1">
    <p>This is my 1st form.</p>
    <button type="submit">Submit Form</button>
</form>

<form action="/Test/2">
    <div>This is my 2nd form.</div>
    <input type="submit" value="Submit Form" />
    <input type="hidden" name="var1" value="123" />
</form>

And I attempt to add an input tag to all forms on the page:

HtmlDocument doc = new HtmlDocument();
doc.LoadHtml(inputHtml); // inputHtml is a string containing the forms above
var nodes = doc.DocumentNode.SelectNodes("//form");
if (nodes != null)
{
    foreach (var node in nodes)
    {
        node.AppendChild(HtmlNode.CreateNode("<input type=\"hidden\" name=\"var2\" value=\"456\" />"));
    }
}
var model = doc.DocumentNode.OuterHtml;

This is what I was expecting:

<form action="/Test/1">
    <p>This is my 1st form.</p>
    <button type="submit">Submit Form</button>
    <input type="hidden" name="var2" value="456">
</form>

<form action="/Test/2">
    <div>This is my 2nd form.</div>
    <input type="submit" value="Submit Form">
    <input type="hidden" name="var1" value="123">
    <input type="hidden" name="var2" value="456">
</form>

However, this is what I get as a result: (line breaks and spacing added for readability)

<form action="/Test/1">
    <input type="hidden" name="var2" value="456">
</form>
    <p>This is my 1st form.</p>
    <button type="submit">Submit Form</button>
</form>

<form action="/Test/2">
    <input type="hidden" name="var2" value="456">
</form>
    <div>This is my 2nd form.</div>
    <input type="submit" value="Submit Form">
    <input type="hidden" name="var1" value="123">
</form>

Now I have duplicate </form> closing tags.

What is the proper way to achieve the desired result using HTML Agility Pack?

Update: 2nd form in expected results had a bug in it showing the duplicate form tag. (Copy-paste error)

Answer 1

Just call HtmlAgilityPack.HtmlNode.ElementsFlags.Remove("form"); before you load your document, after that append should work as you expect.

on a side node:

why bother skipping double quotes when you can write it as:

"<input type='hidden' name='var2' value='456'/>"