ufw allow rules on multiple interfaces

I was trying to set up some rules on multiple interfaces at once with ufw, but had some unsuccessful attempts. Between

This did not open for outgoing traffic on tun0:

$ sudo ufw allow out on tun0,tun1,tun2 to any
$ echo $-
0

But all of a sudden I was able to ping out on tun0 with this one:

$ sudo ufw allow out on tun0
$ echo $-
0

Then to see if my previous tun0,tun1,tun2 wasn’t what I thought it was:

$ sudo ufw allow out on qwerty
$ echo $-
0

What I learned about ufw

• ufw doesn’t care whether an interface name exists or not
• interface names can contain commas
• it’s not possible to configure multiple interfaces in a single rule