title: Running XPath on child node
body: <p>I'm trying to do a xpath lookup on nodes returned by xpath lookup, but it doesn't seem to work as I expected.XPaths executed on the child nodes of a document seem to be executd against hthe root node of the document (in the example, the inventory tag.), instead of the root of the provided node.</p>
  
  <p>Am I missing something here? I'm new to XPath.</p>
  
  <p>Also, please don't answer "just do //book[author='Neal Stephenson'/title". I have a legitimate use case, and this is a simplified example.</p>
  
  <p>Code snippet</p>
  
  <pre><code>DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
  domFactory.setNamespaceAware(true);
  DocumentBuilder builder = domFactory.newDocumentBuilder();
  Document doc = builder.parse("src/main/java/books.xml");
  
  XPathFactory factory = XPathFactory.newInstance();
  XPath xpath = factory.newXPath();
  
  Node book = (Node) xpath.evaluate("//book[author='Neal Stephenson']", doc, XPathConstants.NODE);
  Node title = (Node) xpath.evaluate("/title", book, XPathConstants.NODE); // I get null here.
  Node inventory = (Node) xpath.evaluate("/inventory", book, XPathConstants.NODE); // this returns a node.
  </code></pre>
  
  <p>book.xml</p>
  
  <pre><code>&lt;inventory&gt;
  &lt;book year="2000"&gt;
      &lt;title&gt;Snow Crash&lt;/title&gt;
      &lt;author&gt;Neal Stephenson&lt;/author&gt;
      &lt;publisher&gt;Spectra&lt;/publisher&gt;
      &lt;isbn&gt;0553380958&lt;/isbn&gt;
      &lt;price&gt;14.95&lt;/price&gt;
  &lt;/book&gt;
  
  &lt;book year="2005"&gt;
      &lt;title&gt;Burning Tower&lt;/title&gt;
      &lt;author&gt;Larry Niven&lt;/author&gt;
      &lt;author&gt;Jerry Pournelle&lt;/author&gt;
      &lt;publisher&gt;Pocket&lt;/publisher&gt;
      &lt;isbn&gt;0743416910&lt;/isbn&gt;
      &lt;price&gt;5.99&lt;/price&gt;
  &lt;/book&gt;
  
  &lt;book year="1995"&gt;
      &lt;title&gt;Zodiac&lt;/title&gt;
      &lt;author&gt;Neal Stephenson&lt;/author&gt;
      &lt;publisher&gt;Spectra&lt;/publisher&gt;
      &lt;isbn&gt;0553573862&lt;/isbn&gt;
      &lt;price&gt;7.50&lt;/price&gt;
  &lt;/book&gt;
  
  &lt;!-- more books... --&gt;
  
  &lt;/inventory&gt;
  </code></pre>