title: Syntax error about XPath in Nokogiri, when combining namespace and node()
body: <p>I'm learning XPath with Nokogiri. The XPath is like this:</p>
  
  <pre><code>xml_doc = Nokogiri::XML(open("test.xml"))
  result = xml_doc.xpath("//x:foo", 'x' =&gt; 'www.example.com')
  </code></pre>
  
  <p>I could get the results. But when I perform this call:</p>
  
  <pre><code>result = xml_doc.xpath("//x:node()", 'x' =&gt; 'www.example.com')
  </code></pre>
  
  <p>I get an error:</p>
  
  <pre><code>Nokogiri::XML::XPath::SyntaxError: Invalid expression: //x:node()
  </code></pre>
  
  <p>Am I doing something wrong?</p>