title: Select node with attribute case insensitive via XPath
body: <p>I would like to search node via Xpath case insensitve.</p>
  
  <pre><code>&lt;Validation&gt;
      &lt;Presentation&gt;
          &lt;Slide Tag= "Test"&gt;
              &lt;FontSize Value = "36"/&gt;
          &lt;/Slide&gt;
      &lt;/Presentation&gt;
  &lt;/Validation&gt;
  </code></pre>
  
  <p>I've used this code </p>
  
  <pre><code>String xPath = string.Format("/Validation/Presentation/Slide[lower-case(@Tag)='{0}'][1]", "test");
  XmlNode node = doc.DocumentElement.SelectSingleNode(xPath);
  </code></pre>
  
  <p>but it throws an XPath Exceptions: Namespace Manager or XsltContext needed. This query has a prefix, variable, or user-defined function. Where did I go wrong? </p>