GetElementsByTagName in Htmlagilitypack

How do I select an element for e.g. textbox if I don't know its id?

If I know its id then I can simply write:

HtmlAgilityPack.HtmlNode node = doc.GetElementbyId(id);
 

But I don't know textbox's ID and I can't find GetElementsByTagName method in HtmlagilityPack which is available in webbrowser control.
In web browser control I could have simply written:

HtmlElementCollection elements = browser[i].Document.GetElementsByTagName("form");
 foreach (HtmlElement currentElement in elements)
 {
 
 }
 

EDIT

Here is the HTML form I am talking about

<form id="searchform" method="get" action="/test.php">
 <input name="sometext" type="text">
 </form>
 

Please note I don't know the ID of form. And there can be several forms on same page. The only thing I know is "sometext" and I want to get this element using just this name. So I guess I will have to parse all forms one by one and then find this name "sometext" but how do I do that?

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