Dear Ruo-Xuan Wu,
the additional parameter “rot=0” gives you the option to send this parameter to your function if you’d like to change it (use something else than 0). But if you don’t like to change it you can just ignore this parameter, since it is set to 0 already. In case you never want to use the rotation parameter rot, you don’t need it, but I showed it for an example of how you can add optional parameters (=parameters that you may use or not).
Clear?
Best regards
Reinhard