def find_namespace(dtd)
      return unless dtd.system_id
      dtd_uri = URI.parse(dtd.system_id)
      return unless dtd_uri.path
      @dtd_uri = dtd_uri
      File.basename(@dtd_uri.path, '.dtd')
    end
def find_namespace(dtd)
      return unless dtd.system_id
      dtd_uri = URI.parse(dtd.system_id)
      return unless dtd_uri.path
      @dtd_uri = dtd_uri
      File.basename(@dtd_uri.path, '.dtd')
    end
http://www.w3.org/TR/xhtml1/#dtds