title: XPath Invalid Expression
body: <pre><code>&lt;?php
    $feed = file_get_contents('http://thexmofo.wordpress.com/feed/');
    $xml = new SimpleXMLElement($feed);
    $xml-&gt;registerXPathNamespace('media', 'http://thexmofo.wordpress.com/feed/');
    $images = $xml-&gt;xpath('/rss/channel/item/media:content@url');
    var_dump($images);
  ?&gt;
  </code></pre>
  
  <p>Can anyone tell my why I'm getting <code>Warning: SimpleXMLElement::xpath() [simplexmlelement.xpath]: Invalid expression</code> followed by <code>bool(false)</code>?</p>