Passing an Argument into User Defined Command that's a VBSCript

Greetings Gurus, how do you pass your own arbitrary arguments into a VBScript in a user defined command (as you can with standard commands using the templates and &arg&).

For simplicity I have UDC with one vbscript line: msgbox(&arg&).

https://www.gpsoft.com.au/help/opus12/index.html#!Documents/Scripting/Adding_a_new_Internal_Command.htm

Thanks Leo, that's what I needed.