title: XPath filter by attribute and return distinct values
body: <p>From the following I need to return a distinct list of values with the <code>Category</code> attribute.</p>
  
  <pre><code>&lt;root&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category One&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category One&lt;/classification&gt;
      &lt;/classifications&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category Two&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category One&lt;/classification&gt;
      &lt;/classifications&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category One&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category Two&lt;/classification&gt;
      &lt;/classifications&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category Three&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category One&lt;/classification&gt;
      &lt;/classifications&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category One&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category Two&lt;/classification&gt;
      &lt;/classifications&gt;
      &lt;classifications&gt;
          &lt;classification name="Category"&gt;Category Two&lt;/classification&gt;
          &lt;classification name="Sub-Category"&gt;Sub-Category One&lt;/classification&gt;
      &lt;/classifications&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>Using <code>classifications/classification[@name="Category"]</code> I get:</p>
  
  <pre><code>Category One
  Category Two
  Category One
  Category Three
  Category One
  Category Two
  </code></pre>
  
  <p>What I need is:  </p>
  
  <pre><code>Category One
  Category Two
  Category Three
  </code></pre>