XmlDocument - xpath returns nothing - xpath

Question

I'm trying to read this science.org feed: https://www.science.org/rss/news_current.xml
with this simple code:
using var httpClient = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Get, url);
var response = httpClient.Send(request);
var content = await response.Content.ReadAsStringAsync();
var xmlDoc = new XmlDocument();
xmlDoc.LoadXml(content);
var items = xmlDoc.DocumentElement?.SelectNodes("//item");
if (items != null)
{
Console.WriteLine($"{url}: items={items.Count}");
}
but I get 0 items...
(the 'content' variable is good and contains the right xml data)
It works for other RSS feeds.
any idea of what I'm doing wrong?

Answer 1

Note that the root element includes this default namespace declaration: xmlns="http://purl.org/rss/1.0/", which means that the names of elements within the document are qualified by that namespace URI, unless they have an explicit namespace prefix. Your item elements have no prefix, which means they do belong to that RSS namespace.
So instead of querying for elements named item, you will need to include a namespace prefix in your query, e.g. //rss:item, and of course to allow that prefix to make sense to the SelectNodes method, you'll need to bind the rss prefix to the namespace URI http://purl.org/rss/1.0/. See the documentation for SelectNodes for information about how to handle the namespace.

Answer 2

You can also use XPath 2 and do e.g.
using System.Xml;
using Wmhelp.XPath2;
var doc = new XmlDocument(new NameTable());
doc.Load(#"https://www.science.org/rss/news_current.xml");
var xmlNamespaceMgr = new XmlNamespaceManager(doc.NameTable);
xmlNamespaceMgr.AddNamespace("", "http://purl.org/rss/1.0/");
var items = doc.XPath2SelectNodes("//item", xmlNamespaceMgr);
Console.WriteLine(items.Count);
by using the NuGet package https://www.nuget.org/packages/XPath2.