title: How to select unique nodes
body: <p>I found <a href="http://www.jenitennison.com/xslt/grouping/muenchian.html" rel="noreferrer">this page</a> describing the Muenchian method, but I think I'm applying it wrong.</p>
  
  <p>Consider that this would return a set of ages:</p>
  
  <pre><code>/doc/class/person/descriptive[(@name='age')]/value
  </code></pre>
  
  <blockquote>
    <p>1..2..2..2..3..3..4..7</p>
  </blockquote>
  
  <p>But I would like a nodeset only one node for each age.</p>
  
  <blockquote>
    <p>1..2..3..4..7</p>
  </blockquote>
  
  <p>Each of these seem to return all of the values, instead of unique values:</p>
  
  <pre><code>/doc/class/person/descriptive[(@name='age')][not(value=preceding-sibling::value)]/value
  /doc/class/person/descriptive[(@name='age')]/value[not(value=preceding-sibling::value)]
  </code></pre>
  
  <p>What am I missing?</p>