code: def extract_multiple_numbers(str)
        return [] if str == '' || str.nil?
        str.scan(STDNUMPAT_MULTIPLE).flatten.map{ |i| i.gsub(/\-/, '').upcase }
      end
docs: Extract the most likely looking numbers from the string. This will be each
   string with digits-and-hyphens-and-maybe-a-trailing-X, with the hypens removed
   @param [String] str The string from which to extract the ISBN/ISSNs
   @return [Array] An array of extracted identifiers