title: Find duplicate sibling with xpath
body: <p>How to find only nodes with at least a similar/equal sibling node using Xpath?</p>
  
  <p>For example:</p>
  
  <pre><code>&lt;root&gt;
    &lt;parent&gt;
      &lt;node&gt;...&lt;/node&gt;
      &lt;node_unique&gt;...&lt;/node_unique&gt;
      &lt;node&gt;...&lt;/node&gt;
      &lt;another_one&gt;...&lt;/another_one&gt;
      &lt;another_one&gt;...&lt;/another_one&gt;
    &lt;/parent&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>In the example the xpath shold select only <code>&lt;node&gt;</code> and <code>&lt;another_one&gt;</code> because they are appearing more than once.</p>
  
  <p>I was trying to find a solution for this for hours without success (now I think is not possible with XPath...).</p>