title: XPath query for attribute not starting with another attribute
body: <p>I'm trying to find all people with a displayName that does not start with their preferredName.</p>
  
  <p>e.g.</p>
  
  <pre><code>&lt;people&gt;
    &lt;person displayName="first1 last2" firstName="first1" lastName="last1" preferredName="preferred1" /&gt;
    &lt;person displayName="preferred2 last2" firstName="first2" lastName="last2" preferredName="preferred2" /&gt;
  &lt;/people&gt;
  </code></pre>
  
  <p>I'd like to filter for just the 1st person in this example list.</p>
  
  <p>something like?</p>
  
  <pre><code>/person[not(starts-with(displayName, preferredName))]
  </code></pre>