module Nokogiri::LibXML::XmlXpathContextMixin

def self.included(base)
  base.class_eval do
    layout(
      :doc,  :pointer,
      :node, :pointer
      )
  end
end

def document
  p = self[:doc]
  p.null? ? nil : LibXML::XmlDocumentCast.new(p)
end

def node
  LibXML::XmlNode.new(self[:node])
end