title: Get full path to current node
body: <p>If I have an <code>XPathNavigator</code> positioned on a node, how can I get an XPath expression that represents the path to that node, from the root?</p>
  
  <p>For example, if the XML is:</p>
  
  <pre><code>&lt;data&gt;
      &lt;class name='dogs'&gt;
          &lt;item name='doberman /&gt;
          &lt;item name='husky' /&gt;
      &lt;/class&gt;
      &lt;class name='cats'&gt;
          &lt;item name='persian' /&gt;
          &lt;item name='tabby' /&gt;
      &lt;/class&gt; &lt;/data&gt;
  &lt;/data&gt;
  </code></pre>
  
  <p>...then the path to the persian cat could be expressed as <code>/data/class[2]/item[1]</code></p>
  
  <p>I can enumerate the ancestors of the node in question with <code>SelectAncestors()</code> (or I could iteratively climb up the parent relationship with <code>SelectParent()</code>), but that doesn't get me the positional information. </p>
  
  <p>Would I have to evaluate an XPath using <code>position()</code> for each ancestor, or is there a better way to do this?</p>