class Nokogiri::XML::Document

def wrap doc_struct
  if doc_struct.is_a?(FFI::Pointer)
    # cast native pointers up into a doc cstruct
    return nil if doc_struct.null?
    doc_struct = LibXML::XmlDocument.new(doc_struct)
  end
  doc                  = self.allocate
  doc.cstruct          = doc_struct
  doc.cstruct.ruby_doc = doc
  doc.instance_eval { @decorators = nil; @node_cache = [] }
  doc.send :initialize
  doc
end