def _body
      bitmap  = Bitmap.new
      message = ""
      @values.keys.sort.each do |bmp_num|
        bitmap.set(bmp_num)
        enc_value = @values[bmp_num].encode
        message << enc_value
      end

      if use_hex_bitmap
        [bitmap.to_hex, message]
      else
        [bitmap.to_bytes, message]
      end
    end
def _body
      bitmap  = Bitmap.new
      message = ""
      @values.keys.sort.each do |bmp_num|
        bitmap.set(bmp_num)
        enc_value = @values[bmp_num].encode
        message << enc_value
      end

      if use_hex_bitmap
        [bitmap.to_hex, message]
      else
        [bitmap.to_bytes, message]
      end
    end
METHODS starting with an underscore are meant for
 internal use only ...
 Returns an array of two byte arrays:
 [bitmap_bytes, message_bytes]