C# XPath not selects some child nodes

Question

I'm trying to use the XPath expression: .//*[@class='newsContent newsClosed']/b, but it is not working, always returns 0 elements.

I then tried to change the expression on .//*[@class='newsContent newsClosed'], and it's work.

Why first expression does not work?

I'm using XmlDocument.SelectSingleNode for retrieve elements.

Part of XHTML:

<div class="newsContent newsClosed">
    <b>some text that I need to take</b>
    <br />
    <p>
        text
    </p>
    <p>
        <b>text</b>
        <br />
        <b>text</b>
        <b>text</b>
    </p>
...

In FirePath both expressions are working properly.

Answer 1

Assuming this is XHTML, then you need to specify the namespace of your element: http://www.w3.org/1999/xhtml.

var resolver = new XmlNamespaceManager(new NameTable());

resolver.AddNamespace("html", "http://www.w3.org/1999/xhtml");

var result = doc.SelectSingleNode(
    ".//*[@class='newsContent newsClosed']/html:b", resolver);

My personal preference would be to ditch XPath altogether and use LINQ to XML:

XNamespace html = "http://www.w3.org/1999/xhtml";

var result = (string) doc.Descendants()
    .Where(element => (string) element.Attribute("class") == "newsContent newsClosed")
    .Elements(html + "b")
    .Single();

See this fiddle for a demo.