title: Getting attribute using XPath
body: <p>Given an XML structure like so:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt;
  
  &lt;bookstore&gt;
  
  &lt;book&gt;
    &lt;title lang="eng"&gt;Harry Potter&lt;/title&gt;
    &lt;price&gt;29.99&lt;/price&gt;
  &lt;/book&gt;
  
  &lt;book&gt;
    &lt;title lang="eng"&gt;Learning XML&lt;/title&gt;
    &lt;price&gt;39.95&lt;/price&gt;
  &lt;/book&gt;
  
  &lt;/bookstore&gt;
  </code></pre>
  
  <p>How could I get the value of <code>lang</code> (where <code>lang</code> is <code>eng</code> in book title), for the first element?</p>