title: Find attribute names that start with a certain pattern
body: <p>I am looking to find all attributes of an element that match a certain pattern.</p>
  
  <p>So for an element</p>
  
  <pre><code>&lt;element s2="1" name="aaaa" id="1" /&gt;
  &lt;element s3="1" name="aaaa" id="2" /&gt;
  </code></pre>
  
  <p>I would like to be able to find all attributes that start with 's' (returning the value of <strong>s1</strong> for the first element and <strong>s3</strong> for the value of the second element).</p>
  
  <p>If this is outside of xpath's ability please let me know.</p>