title: Undefined namespace prefix in Nokogiri and XPath
body: <p>I am trying to parse Youtube Gdata to see if video with given id exists. But there isn't normal tag but with namespace. On the link <a href="http://gdata.youtube.com/feeds/api/videos?q=KgfdlZuVz7I">http://gdata.youtube.com/feeds/api/videos?q=KgfdlZuVz7I</a> there is tag:</p>
  
  <pre><code>&lt;openSearch:totalResults&gt;1&lt;/openSearch:totalResults&gt;
  </code></pre>
  
  <p>There is namespace openSearch:</p>
  
  <pre><code>xmlns:openSearch='http://a9.com/-/spec/opensearchrss/1.0/'
  </code></pre>
  
  <p>but I dont know how to deal with it in Nokogiri and Ruby.</p>
  
  <p>Here is part of code:</p>
  
  <pre><code>xmlfeed = Nokogiri::HTML(open("http://gdata.youtube.com/feeds/api/videos?q=#{video_id}"))
  xmlfeed.at_xpath("openSearch:totalResults")
  </code></pre>
  
  <p>It gives error:</p>
  
  <pre><code>Undefined namespace prefix: openSearch:totalResults
  </code></pre>