TFTP with folder and regexp

RouterOS General
1

Hi people,
I want to use a regexp to send a config file for one MAC:

/ip tftp add req-filename=“^cfg(0-9a-f+).xml$” real-filename=“/disk1/mac/cfg\1.xml” allow=yes read-only=yes

But, I don’t understant the documentation https://wiki.mikrotik.com/wiki/Manual:IP/TFTP:
real-filename format for using multiple regex is filename\0\5\6
What does it mean “\0\5\6” ?

Thanks