title: how to format SelectSingleNode xPath with index #?
body: <p>i want to SelectSingleNode with index # since i have few elements with the same path.</p>
  
  <pre><code>xDoc.DocumentElement.SelectSingleNode(xPath).InnerText = xValue.ToString();
  </code></pre>
  
  <p>When xPath is the following string:</p>
  
  <p>"/Parameter [@tag='tool_od']/Value/ValueSeries/<strong>Value[Index=1]</strong>/value"</p>
  
  <p>or
  "/Parameter [@tag='tool_od']/Value/ValueSeries/<strong>Value[1]</strong>/value"</p>
  
  <p>or 
  "/Parameter [@tag='tool_od']/Value/ValueSeries/<strong>Value[@Index=1]</strong>/value"</p>
  
  <p>all of those options gives me an error:
  "Object reference not set to an instance of an object."</p>
  
  <p>this is the part of the xml:
  i want to be able to access each of  childs with selectsinglenode.</p>
  
  <pre><code>&lt;ValueSeries&gt;
              &lt;Value&gt;
                &lt;value&gt;25&lt;/value&gt;
              &lt;/Value&gt;
              &lt;Value&gt;
                &lt;value&gt;999012.0&lt;/value&gt;
              &lt;/Value&gt;
              &lt;Value&gt;
                &lt;value&gt;999012.0&lt;/value&gt;
              &lt;/Value&gt;
  &lt;/ValueSeries&gt;
  </code></pre>
  
  <p>if i will remove the index part the path will work fine but it will only access the first element  and not the others.</p>