title: Why XPath expression doesn't return any results in C# but it does outside C#?
body: <p>I'm working on Open XML document format for excel sheets.</p>
  
  <pre><code>var nodeList = WorksheetXml.SelectNodes(@"//c[child::f]");
  </code></pre>
  
  <p>it should return all rows with formulas, but it doesn't return anything. The same xml on Oxygen Editor, when applied the same xpath expression, returns all of them.</p>
  
  <p>I am copying WorksheetXml inner xml to assure the content is the same... do you know why C# is not working the expected way?</p>
  
  <hr>
  
  <p>EDIT: Namespace issue</p>
  
  <p>I've put this:</p>
  
  <pre><code>var manager = new XmlNamespaceManager(WorksheetXml.NameTable);
  manager.AddNamespace(string.Empty, @"http://schemas.openxmlformats.org/spreadsheetml/2006/main");
  manager.AddNamespace("r", @"http://schemas.openxmlformats.org/officeDocument/2006/relationships");
  
  var nodeList = WorksheetXml.SelectNodes(@"//c[child::f]", manager);
  </code></pre>
  
  <p>and it didn't work, I think it is not a namespace problem.</p>